Nextcloud Client hangs under macOS Catalina

For the last couple of weeks, my Nextcloud client (v3.3.6, the most current available for download) has been hanging on my Mac (running macOS Catalina 10.15.7). I’m running Nextcloud server 22.2.3 on my own server. The client doesn’t sync, show a menu bar icon, show a dialog, or appear to do anything else–it just sits there consuming one full core of CPU:
image

I can kill that process and re-launch the application, but it does the same thing (though occasionally without taking 100% CPU). I’ve tried reinstalling the client–the new installation continues to behave the same way. I’ve rebooted several times–each time I reboot, the client auto-starts as it should, but continues to behave in the same way. I don’t see anything in the Console application logging errors–at least that I understand–with Nextcloud:

default	06:29:18.511447-0500	runningboardd	[executable<Nextcloud(501)>:1139] Death sentinel fired!
default	06:29:18.516514-0500	runningboardd	Invalidating assertion 474-174-303 (target:executable<Nextcloud(501)>) from originator 174
default	06:29:18.518186-0500	loginwindow	-[PersistentAppsSupport applicationQuit:] | for app:Nextcloud, _appTrackingState = 2
default	06:29:18.619658-0500	runningboardd	Removing process: [executable<Nextcloud(501)>:1139]
default	06:29:18.620167-0500	runningboardd	Removing assertions for terminated process: [executable<Nextcloud(501)>:1139]
error	06:29:18.628571-0500	runningboardd	RBSStateCapture remove item called for untracked item 474-174-303 (target:executable<Nextcloud(501)>)
error	06:29:19.300829-0500	FinderSyncExt	An uncaught exception was raised
error	06:29:19.300914-0500	FinderSyncExt	An uncaught exception was raised
error	06:29:19.300875-0500	FinderSyncExt	connection went invalid while waiting for a reply because a mach port died
error	06:29:19.300961-0500	FinderSyncExt	connection went invalid while waiting for a reply because a mach port died
error	06:29:19.301249-0500	FinderSyncExt	(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x000000010de3f8a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x000000010de4064a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRequestWithExtensionItems:listenerEndpoint:withContextUUID:completion:]_block_invoke + 868
	9   libdispatch.dylib                   0x00007fff698466c4 _dispatch_call_block_and_release + 12
	10  libdispatch.dylib                   0x00007fff69847658 _dispatch_client_callout + 8
	11  libdispatch.dylib                   0x00007fff69852cab _dispatch_main_queue_callback_4CF + 936
	12  CoreFoundation                      0x00007fff2f738e81 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
	13  CoreFoundation                      0x00007fff2f6f8c87 __CFRunLoopRun + 2028
	14  CoreFoundation                      0x00007fff2f6f7e3e CFRunLoopRunSpecific + 462
	15  HIToolbox                           0x00007fff2e324abd RunCurrentEventLoopInMode + 292
	16  HIToolbox                           0x00007fff2e3247d5 ReceiveNextEventCommon + 584
	17  HIToolbox                           0x00007fff2e324579 _BlockUntilNextEventMatchingListInModeWithFilter + 64
	18  AppKit                              0x00007fff2c96a039 _DPSNextEvent + 883
	19  AppKit                              0x00007fff2c968880 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1352
	20  AppKit                              0x00007fff2c95a58e -[NSApplication run] + 658
	21  AppKit                              0x00007fff2c92c396 NSApplicationMain + 777
	22  libxpc.dylib                        0x00007fff69aff944 _xpc_objc_main.cold.3 + 56
	23  libxpc.dylib                        0x00007fff69aee462 _xpc_objc_main + 609
	24  libxpc.dylib                        0x00007fff69aedf63 _xpc_copy_xpcservice_dictionary + 0
	25  Foundation                          0x00007fff31dcee6f +[NSXPCListener serviceListener] + 0
	26  PlugInKit                           0x00007fff5a588ecb __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31851
	27  PlugInKit                           0x00007fff5a588bf4 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31124
	28  PlugInKit                           0x00007fff5a5892b2 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 32850
	29  Foundation                          0x00007fff31e47b4c NSExtensionMain + 49
	30  libdyld.dylib                       0x00007fff698a0cc9 start + 1
)
error	06:29:19.301362-0500	FinderSyncExt	(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x000000010fdbf8a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x000000010fdc064a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRequestWithExtensionItems:listenerEndpoint:withContextUUID:completion:]_block_invoke + 868
	9   libdispatch.dylib                   0x00007fff698466c4 _dispatch_call_block_and_release + 12
	10  libdispatch.dylib                   0x00007fff69847658 _dispatch_client_callout + 8
	11  libdispatch.dylib                   0x00007fff69852cab _dispatch_main_queue_callback_4CF + 936
	12  CoreFoundation                      0x00007fff2f738e81 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
	13  CoreFoundation                      0x00007fff2f6f8c87 __CFRunLoopRun + 2028
	14  CoreFoundation                      0x00007fff2f6f7e3e CFRunLoopRunSpecific + 462
	15  HIToolbox                           0x00007fff2e324abd RunCurrentEventLoopInMode + 292
	16  HIToolbox                           0x00007fff2e3247d5 ReceiveNextEventCommon + 584
	17  HIToolbox                           0x00007fff2e324579 _BlockUntilNextEventMatchingListInModeWithFilter + 64
	18  AppKit                              0x00007fff2c96a039 _DPSNextEvent + 883
	19  AppKit                              0x00007fff2c968880 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1352
	20  AppKit                              0x00007fff2c95a58e -[NSApplication run] + 658
	21  AppKit                              0x00007fff2c92c396 NSApplicationMain + 777
	22  libxpc.dylib                        0x00007fff69aff944 _xpc_objc_main.cold.3 + 56
	23  libxpc.dylib                        0x00007fff69aee462 _xpc_objc_main + 609
	24  libxpc.dylib                        0x00007fff69aedf63 _xpc_copy_xpcservice_dictionary + 0
	25  Foundation                          0x00007fff31dcee6f +[NSXPCListener serviceListener] + 0
	26  PlugInKit                           0x00007fff5a588ecb __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31851
	27  PlugInKit                           0x00007fff5a588bf4 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31124
	28  PlugInKit                           0x00007fff5a5892b2 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 32850
	29  Foundation                          0x00007fff31e47b4c NSExtensionMain + 49
	30  libdyld.dylib                       0x00007fff698a0cc9 start + 1
)
default	06:29:19.301460-0500	FinderSyncExt	*** Terminating app due to uncaught exception 'NSInvalidReceivePortException', reason: 'connection went invalid while waiting for a reply because a mach port died'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x000000010de3f8a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x000000010de4064a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRe<…>
default	06:29:19.302187-0500	runningboardd	[xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:2734] Death sentinel fired!
default	06:29:19.302290-0500	FinderSyncExt	*** Terminating app due to uncaught exception 'NSInvalidReceivePortException', reason: 'connection went invalid while waiting for a reply because a mach port died'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x000000010fdbf8a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x000000010fdc064a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRe<…>
default	06:29:19.303124-0500	runningboardd	[xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:1167] Death sentinel fired!
default	06:29:19.306818-0500	loginwindow	-[PersistentAppsSupport applicationQuit:] | for app:Nextcloud Extensions, _appTrackingState = 2
default	06:29:19.306988-0500	runningboardd	Invalidating assertion 474-174-1005 (target:xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>) from originator 174
default	06:29:19.309680-0500	loginwindow	-[PersistentAppsSupport applicationQuit:] | for app:Nextcloud Extensions, _appTrackingState = 2
default	06:29:19.309581-0500	runningboardd	Invalidating assertion 474-174-169 (target:xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>) from originator 174
default	06:29:19.403585-0500	runningboardd	Removing process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:1167]
default	06:29:19.403585-0500	runningboardd	Removing process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:2734]
default	06:29:19.404560-0500	runningboardd	Removing assertions for terminated process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:1167]
default	06:29:19.419015-0500	runningboardd	Removing assertions for terminated process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:2734]
error	06:29:19.419018-0500	runningboardd	RBSStateCapture remove item called for untracked item 474-174-169 (target:xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>)
error	06:29:19.724817-0500	FinderSyncExt	An uncaught exception was raised
error	06:29:19.724891-0500	FinderSyncExt	connection went invalid while waiting for a reply because a mach port died
error	06:29:19.725346-0500	FinderSyncExt	(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x0000000106ae88a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x0000000106ae964a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRequestWithExtensionItems:listenerEndpoint:withContextUUID:completion:]_block_invoke + 868
	9   libdispatch.dylib                   0x00007fff698466c4 _dispatch_call_block_and_release + 12
	10  libdispatch.dylib                   0x00007fff69847658 _dispatch_client_callout + 8
	11  libdispatch.dylib                   0x00007fff69852cab _dispatch_main_queue_callback_4CF + 936
	12  CoreFoundation                      0x00007fff2f738e81 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
	13  CoreFoundation                      0x00007fff2f6f8c87 __CFRunLoopRun + 2028
	14  CoreFoundation                      0x00007fff2f6f7e3e CFRunLoopRunSpecific + 462
	15  HIToolbox                           0x00007fff2e324abd RunCurrentEventLoopInMode + 292
	16  HIToolbox                           0x00007fff2e3247d5 ReceiveNextEventCommon + 584
	17  HIToolbox                           0x00007fff2e324579 _BlockUntilNextEventMatchingListInModeWithFilter + 64
	18  AppKit                              0x00007fff2c96a039 _DPSNextEvent + 883
	19  AppKit                              0x00007fff2c968880 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1352
	20  AppKit                              0x00007fff2c95a58e -[NSApplication run] + 658
	21  AppKit                              0x00007fff2c92c396 NSApplicationMain + 777
	22  libxpc.dylib                        0x00007fff69aff944 _xpc_objc_main.cold.3 + 56
	23  libxpc.dylib                        0x00007fff69aee462 _xpc_objc_main + 609
	24  libxpc.dylib                        0x00007fff69aedf63 _xpc_copy_xpcservice_dictionary + 0
	25  Foundation                          0x00007fff31dcee6f +[NSXPCListener serviceListener] + 0
	26  PlugInKit                           0x00007fff5a588ecb __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31851
	27  PlugInKit                           0x00007fff5a588bf4 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 31124
	28  PlugInKit                           0x00007fff5a5892b2 __PLUGINKIT_CALLING_OUT_TO_CLIENT_SUBSYSTEM_FOR_BEGINUSING__ + 32850
	29  Foundation                          0x00007fff31e47b4c NSExtensionMain + 49
	30  libdyld.dylib                       0x00007fff698a0cc9 start + 1
)
default	06:29:19.725604-0500	FinderSyncExt	*** Terminating app due to uncaught exception 'NSInvalidReceivePortException', reason: 'connection went invalid while waiting for a reply because a mach port died'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff2f775b57 __exceptionPreprocess + 250
	1   libobjc.A.dylib                     0x00007fff686f85bf objc_exception_throw + 48
	2   Foundation                          0x00007fff31e7fc8b -[NSConnection sendInvocation:internal:] + 2990
	3   CoreFoundation                      0x00007fff2f6da165 ___forwarding___ + 829
	4   CoreFoundation                      0x00007fff2f6d9d98 _CF_forwarding_prep_0 + 120
	5   Foundation                          0x00007fff31e7ede2 -[NSConnection rootProxy] + 52
	6   FinderSyncExt                       0x0000000106ae88a0 -[SyncClientProxy start] + 169
	7   FinderSyncExt                       0x0000000106ae964a -[FinderSync init] + 825
	8   Foundation                          0x00007fff31e48b3c __105-[_NSExtensionContextVendor _beginRe<…>
default	06:29:19.726459-0500	runningboardd	[xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:25626] Death sentinel fired!
default	06:29:19.730469-0500	loginwindow	-[PersistentAppsSupport applicationQuit:] | for app:Nextcloud Extensions, _appTrackingState = 2
default	06:29:19.730737-0500	runningboardd	Invalidating assertion 474-174-12567 (target:xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>) from originator 174
default	06:29:19.832437-0500	runningboardd	Removing process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:25626]
default	06:29:19.833055-0500	runningboardd	Removing assertions for terminated process: [xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>:25626]
error	06:29:19.843185-0500	runningboardd	RBSStateCapture remove item called for untracked item 474-174-12567 (target:xpcservice<com.nextcloud.desktopclient.FinderSyncExt(501)>)
default	06:29:22.493119-0500	ReportCrash	Sending event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.493269-0500	analyticsd	Received event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.493442-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3 Dirty: 7 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562493044}
default	06:29:22.493545-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3WithIncidentID Dirty: 7 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562493044}
default	06:29:22.706221-0500	ReportCrash	Sending event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.706437-0500	analyticsd	Received event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.706602-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3 Dirty: 8 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562706040}
default	06:29:22.706724-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3WithIncidentID Dirty: 8 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562706040}
default	06:29:22.969762-0500	ReportCrash	Sending event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.970033-0500	analyticsd	Received event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt"}
default	06:29:22.970243-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3 Dirty: 9 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562969612}
default	06:29:22.970387-0500	analyticsd	Aggregated. Transform: StabilityCrashNumerator3WithIncidentID Dirty: 9 Event: com.apple.stability.crash {"appVersion":"1.0","bundleID":"com.nextcloud.desktopclient.FinderSyncExt","exceptionType":13,"process":"FinderSyncExt","responsibleApp":"FinderSyncExt","timestamp":1639740562969612}
default	06:29:36.269247-0500	distnoted	register name: com.apple.sharedfilelist.change object: com.apple.LSSharedFileList.ApplicationRecentDocuments/com.nextcloud.desktopclient token: f4a89 pid: 779
default	06:29:36.285023-0500	distnoted	register name: com.apple.sharedfilelist.change object: com.apple.LSSharedFileList.ApplicationRecentDocuments/com.nextcloud.desktopclient token: f4a8f pid: 779
default	06:29:36.749979-0500	Spotlight	LAUNCHING:0x0-0x1835834 nextcloud foreground=0 bringForward=0 seed=312 userActivityCount=0
default	06:29:36.764827-0500	loginwindow	-[ApplicationManager checkInAppContext:eventData:] | ApplicationManager: Checked in app : nextcloud
default	06:29:36.765377-0500	runningboardd	Resolved pid 26001 to [executable<Nextcloud(501)>:26001]
default	06:29:36.767386-0500	runningboardd	[executable<Nextcloud(501)>:26001] This process will not be managed.
default	06:29:36.767425-0500	runningboardd	Now tracking process: [executable<Nextcloud(501)>:26001]
default	06:29:36.768043-0500	runningboardd	Acquiring assertion targeting executable<Nextcloud(501)> from originator [daemon<com.apple.coreservices.launchservicesd>:174] with description <RBSAssertionDescriptor; uielement:26001; ID: 474-174-12779; target: 26001> attributes = {
    <RBSDomainAttribute: 0x7fe73aa13130; domain: com.apple.launchservicesd; name: RoleUserInteractive; sourceEnvironment: 0x0>;
}
default	06:29:36.768198-0500	runningboardd	Assertion 474-174-12779 (target:executable<Nextcloud(501)>) will be created as active
default	06:29:36.768692-0500	runningboardd	Acquiring assertion targeting executable<Nextcloud(501)> from originator [daemon<com.apple.coreservices.launchservicesd>:174] with description <RBSAssertionDescriptor; uielement:26001; ID: 474-174-12780; target: 26001> attributes = {
    <RBSDomainAttribute: 0x7fe738d25850; domain: com.apple.launchservicesd; name: RoleUserInteractive; sourceEnvironment: 0x0>;
}
default	06:29:36.768709-0500	runningboardd	[executable<Nextcloud(501)>:26001] Ignoring jetsam update because this process is not memory-managed
default	06:29:36.768860-0500	runningboardd	[executable<Nextcloud(501)>:26001] Ignoring resume because this process is not lifecycle managed
default	06:29:36.768865-0500	runningboardd	Assertion 474-174-12780 (target:executable<Nextcloud(501)>) will be created as active
default	06:29:36.768943-0500	runningboardd	[executable<Nextcloud(501)>:26001] Set darwin role to: UserInteractive
default	06:29:36.769006-0500	runningboardd	Finished acquiring assertion 474-174-12779 (target:executable<Nextcloud(501)>)
default	06:29:36.769033-0500	runningboardd	[executable<Nextcloud(501)>:26001] Ignoring GPU update because this process is not GPU managed
default	06:29:36.769676-0500	runningboardd	Finished acquiring assertion 474-174-12780 (target:executable<Nextcloud(501)>)
default	06:29:36.769685-0500	runningboardd	Invalidating assertion 474-174-12779 (target:executable<Nextcloud(501)>) from originator 174
default	06:29:36.862725-0500	Nextcloud	FRONTLOGGING: version 1
default	06:29:36.862912-0500	Nextcloud	Registering, pid=26001
default	06:29:36.864733-0500	Nextcloud	CHECKIN: pid=26001
default	06:29:36.880542-0500	Nextcloud	CHECKEDIN: pid=26001 asn=0x0-0x1835834 foreground=0
default	06:29:36.880377-0500	launchservicesd	CHECKIN:0x0-0x1835834 26001 com.nextcloud.desktopclient
default	06:29:36.881654-0500	loginwindow	-[ApplicationManager checkInAppContext:eventData:] | ApplicationManager: Checked in app : Nextcloud
default	06:29:36.893582-0500	Nextcloud	Registered, pid=26001 ASN=0x0,0x1835834
default	06:29:36.893758-0500	Nextcloud	Registered, pid=26001 cgConnectionID=86713
default	06:29:36.895205-0500	Nextcloud	BringForward: pid=26001 asn=0x0-0x1835834 bringForward=0 foreground=0 uiElement=1 launchedByLS=1 modifiersCount=1 allDisabled=0
default	06:29:36.895281-0500	Nextcloud	BringFrontModifier: pid=26001 asn=0x0-0x1835834 Modifier 0 hideAfter=0 hideOthers=0 dontMakeFrontmost=0 mouseDown=0/0 seed=0/0
default	06:29:36.896104-0500	Nextcloud	Current system appearance, (HLTB: 2), (SLS: 1)
default	06:29:36.900036-0500	Nextcloud	Post-registration system appearance: (HLTB: 2)
default	06:29:36.910492-0500	distnoted	register name: com.apple.xctest.FakeForceTouchDevice object: com.nextcloud.desktopclient token: f4268 pid: 26001
default	06:29:36.914352-0500	Nextcloud	Registering for test daemon availability notify post.
default	06:29:36.914510-0500	Nextcloud	notify_get_state check indicated test daemon not ready.
default	06:29:36.925947-0500	Nextcloud	NSApp cache appearance:
-NSRequiresAquaSystemAppearance: 0
-appearance: (null)
-effectiveAppearance: <NSCompositeAppearance: 0x60000111b280
 (
    "<NSDarkAquaAppearance: 0x600001108d00>",
    "<NSSystemAppearance: 0x600001108d80>"
)>
default	06:29:46.918961-0500	Nextcloud	LSExceptions shared instance invalidated for timeout.

Kind of at a loss for what else to be checking here–any suggestions?

Edit: Poking around through the nextcloud.app contents, I see the nextcloudcmd binary. So let’s try it:

 ✘ dan@tardis  /Applications/nextcloud.app/Contents/MacOS  ./nextcloudcmd --logdebug ~/Nextcloud https://db-cloud.org
2021-12-17 07:49:15:165 [ debug default /var/folders/yr/9dx0mtfj7kdf4725tmcz6md80000gp/T/macos-8401/src/libsync/logger.cpp:228 ]	[ OCC::Logger::setLogRules ]:	"nextcloud.*.debug=true\n"
12-17 07:49:15:282 [ warning qt.network.ssl ]:	Error receiving trust for a CA certificate
12-17 07:49:15:285 [ warning qt.network.ssl ]:	Error receiving trust for a CA certificate
12-17 07:49:15:287 [ warning qt.network.ssl ]:	Error receiving trust for a CA certificate
Please enter user name: ***
Password for user ***: [1]    29591 segmentation fault  ./nextcloudcmd --logdebug ~/Nextcloud https://db-cloud.org

Edit 2: and notwithstanding the error message reported above, the system is serving a current, valid Let’s Encrypt cert.

I had a similar problem for the past month or so, more or less since I installed client version 3.4.x (might have started at 3.4.1): sync would get stuck with high CPU usage and “not responding” red line in Activity Monitor.
The fun thing is: I tried to run the command line client in debug mode as you show and… it run correctly plus after that the regular client too started again to work without getting stuck.

I suspect there was a file with some illegal filename that now is synced… but how to find it?