It happens regularly that the desktop client does not re-establish its own connection to NCP after the daily re-establishment of the connection of the router with the Internet. A connection problem is entered in the log and then the same error messages are entered endlessly in the log. The only thing that helps is to stop the client and restart it again.
Here are the corresponding entries from the log of the desktop client. I have replaced some information with corresponding terms in angle brackets.
2021-05-06 01:17:41:293 [ info nextcloud.sync.networkjob.etag ]: Request Etag of QUrl(“https://.myfritz.net/remote.php/dav/files//”) FINISHED WITH STATUS “OK”
2021-05-06 01:17:41:293 [ debug nextcloud.sync.networkjob ] [ OCC::AbstractNetworkJob::slotFinished ]: Network job OCC::RequestEtagJob finished for “/”
2021-05-06 01:18:10:989 [ info nextcloud.gui.folder.manager ]: Etag poll timer timeout
2021-05-06 01:18:10:989 [ info nextcloud.gui.folder.manager ]: Folders to sync: 1
2021-05-06 01:18:10:989 [ info nextcloud.gui.folder.manager ]: Number of folders that don’t use push notifications: 1
2021-05-06 01:18:10:989 [ info nextcloud.gui.folder.manager ]: Run etag job on folder OCC::Folder(0x1a9a29f2020)
2021-05-06 01:18:10:989 [ info nextcloud.gui.folder ]: Trying to check “https://.myfritz.net/remote.php/dav/files//” for changes via ETag check. (time since last sync: 4449 s)
2021-05-06 01:18:10:989 [ debug nextcloud.gui.folder.manager ] [ OCC::FolderMan::slotRunOneEtagJob ]: Scheduling “https://.myfritz.net/remote.php/dav/files//” to check remote ETag
2021-05-06 01:18:10:989 [ info nextcloud.sync.accessmanager ]: 6 “PROPFIND” “https://.myfritz.net/remote.php/dav/files//” has X-Request-ID “1db12d1a-c137-4bb8-a4c1-60fe751936db”
2021-05-06 01:18:10:989 [ debug nextcloud.sync.cookiejar ] [ OCC::CookieJar::cookiesForUrl ]: QUrl(“https://.myfritz.net/remote.php/dav/files//”) requests: (QNetworkCookie("__Host-nc_sameSiteCookielax=true; secure; HttpOnly; expires=Fri, 31-Dec-2100 23:59:59 GMT; domain=.myfritz.net; path=/"), QNetworkCookie("__Host-nc_sameSiteCookiestrict=true; secure; HttpOnly; expires=Fri, 31-Dec-2100 23:59:59 GMT; domain=.myfritz.net; path=/"), QNetworkCookie(“oc_sessionPassphrase=; secure; HttpOnly; domain=.myfritz.net; path=/”), QNetworkCookie(“oclaqn5ofjmm=tdk0b5he5gb4k25b7p5u0nikk9; secure; HttpOnly; domain=.myfritz.net; path=/”))
2021-05-06 01:18:10:989 [ info nextcloud.sync.networkjob ]: OCC::RequestEtagJob created for “https://.myfritz.net” + “/” “OCC::Folder”
2021-05-06 01:18:26:787 [ debug nextcloud.sync.connectionvalidator ] [ OCC::ConnectionValidator::checkAuthentication ]: # Check whether authenticated propfind works.
2021-05-06 01:18:26:787 [ info nextcloud.sync.accessmanager ]: 6 “PROPFIND” “https://.myfritz.net/remote.php/dav/files//” has X-Request-ID “5e4e7927-49d7-45a7-a2c6-6d3657398d27”
2021-05-06 01:18:26:787 [ debug nextcloud.sync.cookiejar ] [ OCC::CookieJar::cookiesForUrl ]: QUrl(“https://.myfritz.net/remote.php/dav/files//”) requests: (QNetworkCookie("__Host-nc_sameSiteCookielax=true; secure; HttpOnly; expires=Fri, 31-Dec-2100 23:59:59 GMT; domain=.myfritz.net; path=/"), QNetworkCookie("__Host-nc_sameSiteCookiestrict=true; secure; HttpOnly; expires=Fri, 31-Dec-2100 23:59:59 GMT; domain=.myfritz.net; path=/"), QNetworkCookie(“oc_sessionPassphrase=; secure; HttpOnly; domain=.myfritz.net; path=/”), QNetworkCookie(“oclaqn5ofjmm=tdk0b5he5gb4k25b7p5u0nikk9; secure; HttpOnly; domain=.myfritz.net; path=/”))
2021-05-06 01:18:26:787 [ info nextcloud.sync.networkjob ]: OCC::PropfindJob created for “https://.myfritz.net” + “/” “OCC::ConnectionValidator”
2021-05-06 01:18:26:840 [ info nextcloud.sync.credentials.webflow ]: request finished
2021-05-06 01:18:26:840 [ warning nextcloud.sync.networkjob ]: SslHandshakeFailedError: “Im Ablauf des SSL-Protokolls ist ein Fehler aufgetreten.” : can be caused by a webserver wanting SSL client certificates
2021-05-06 01:18:26:840 [ warning nextcloud.sync.networkjob ]: QNetworkReply::SslHandshakeFailedError “Im Ablauf des SSL-Protokolls ist ein Fehler aufgetreten.” QVariant(Invalid)
2021-05-06 01:18:26:840 [ warning nextcloud.sync.credentials.webflow ]: QNetworkReply::SslHandshakeFailedError
2021-05-06 01:18:26:840 [ warning nextcloud.sync.credentials.webflow ]: “Im Ablauf des SSL-Protokolls ist ein Fehler aufgetreten.”
2021-05-06 01:18:26:840 [ info nextcloud.sync.networkjob.propfind ]: PROPFIND of QUrl(“https://.myfritz.net/remote.php/dav/files//”) FINISHED WITH STATUS “SslHandshakeFailedError Im Ablauf des SSL-Protokolls ist ein Fehler aufgetreten.”
2021-05-06 01:18:26:840 [ warning nextcloud.sync.networkjob.propfind ]: not successful, http result code is 0 “”
2021-05-06 01:18:26:840 [ info nextcloud.gui.account.state ]: AccountState connection status change: OCC::ConnectionValidator::Connected → OCC::ConnectionValidator::SslError
2021-05-06 01:18:26:840 [ info nextcloud.gui.account.state ]: AccountState state change: “Verbunden” → “Abgemeldet”
2021-05-06 01:18:26:840 [ debug nextcloud.gui.socketapi ] [ OCC::SocketListener::sendMessage ]: Sending SocketAPI message → “UNREGISTER_PATH:O:\Nextcloud” to QLocalSocket(0x1a9a313a520)
2021-05-06 01:18:26:872 [ info nextcloud.gui.folder.manager ]: Account “@.myfritz.net” disconnected or paused, terminating or descheduling sync folders
2021-05-06 01:18:26:872 [ debug nextcloud.sync.networkjob ] [ OCC::AbstractNetworkJob::slotFinished ]: Network job OCC::PropfindJob finished for “/”
2021-05-06 01:18:40:997 [ info nextcloud.gui.folder.manager ]: Etag poll timer timeout
2021-05-06 01:18:40:997 [ info nextcloud.gui.folder.manager ]: Folders to sync: 1
2021-05-06 01:18:40:997 [ info nextcloud.gui.folder.manager ]: Number of folders that don’t use push notifications: 1
2021-05-06 01:18:40:997 [ info nextcloud.gui.folder.manager ]: Run etag job on folder OCC::Folder(0x1a9a29f2020)
2021-05-06 01:18:40:997 [ info nextcloud.gui.folder.manager ]: Can not run etag job: Folder is busy
2021-05-06 01:19:11:000 [ warning nextcloud.sync.networkjob ]: Network job timeout QUrl(“https://.myfritz.net/remote.php/dav/files//”)
2021-05-06 01:19:11:000 [ info nextcloud.sync.credentials.webflow ]: request finished
2021-05-06 01:19:11:000 [ warning nextcloud.sync.networkjob ]: QNetworkReply::OperationCanceledError “Zeitüberschreitung bei der Verbindung” QVariant(Invalid)
2021-05-06 01:19:11:000 [ warning nextcloud.sync.credentials.webflow ]: QNetworkReply::OperationCanceledError
2021-05-06 01:19:11:000 [ warning nextcloud.sync.credentials.webflow ]: “Operation abgebrochen”
2021-05-06 01:19:11:000 [ info nextcloud.sync.networkjob.etag ]: Request Etag of QUrl(“https://.myfritz.net/remote.php/dav/files//”) FINISHED WITH STATUS “OperationCanceledError Zeitüberschreitung bei der Verbindung”
2021-05-06 01:19:11:000 [ debug nextcloud.sync.networkjob ] [ OCC::AbstractNetworkJob::slotFinished ]: Network job OCC::RequestEtagJob finished for “/”
2021-05-06 01:19:11:000 [ info nextcloud.gui.folder.manager ]: Etag poll timer timeout
2021-05-06 01:19:11:000 [ info nextcloud.gui.folder.manager ]: Folders to sync: 1
2021-05-06 01:19:11:000 [ info nextcloud.gui.folder.manager ]: Number of folders that don’t use push notifications: 1
2021-05-06 01:19:11:000 [ info nextcloud.gui.folder.manager ]: Run etag job on folder OCC::Folder(0x1a9a29f2020)
2021-05-06 01:19:11:000 [ info nextcloud.gui.folder.manager ]: Can not run etag job: Folder is busy
2021-05-06 01:19:41:017 [ info nextcloud.gui.folder.manager ]: Etag poll timer timeout
2021-05-06 01:19:41:017 [ info nextcloud.gui.folder.manager ]: Folders to sync: 1
2021-05-06 01:19:41:017 [ info nextcloud.gui.folder.manager ]: Number of folders that don’t use push notifications: 1
2021-05-06 01:19:41:017 [ info nextcloud.gui.folder.manager ]: Run etag job on folder OCC::Folder(0x1a9a29f2020)
2021-05-06 01:19:41:017 [ info nextcloud.gui.folder.manager ]: Can not run etag job: Folder is busy
2021-05-06 01:20:11:037 [ info nextcloud.gui.folder.manager ]: Etag poll timer timeout
… and so on…