Nexcloud client hangs with file synchronization

Nextcloud server: NexcloudPi v.1.55.3 under Debian Bookworm
Nextcloud client: Version 3.15.3 (Flatpak) under Linux Mint 22 Wilma
Both systems are up to date and are in the same LAN.

The Nextcloud client is hanging while synchronizing files, it stays with the remark “synchronizing file 0 of 146” with no progress.
This configuration was used without problems for many months already, it looks like the problem occured at an update sometime in December.

The Nextcloud server on the Raspberry seems to work fine, updates of Adresses and Calendars is working well from this Linux Mint desktop system.
Also file synchronization from my other Notebook (also Linux Mint) to the NCP server are working without issues, as well as uploads from my iphone.

Is there any chance to fix this issue without re-installation of the client ? I want to avoid synchronizing hundreds of GB again with the rel. slow NCP.

Thank you!

Hello,

Would the following data from the log files of the client help ?

2025-01-26 20:18:48:225 [ info nextcloud.sync.account /run/build/nextcloud-client/src/libsync/account.cpp:571 ]: ssl errors “SSL-Errors happened for url "https://192.168.170.43/ocs/v2.php/apps/user_status/api/v1/user_status?format=json\” \tError in QSslCertificate(Version="3", SerialNumber="28:9d:89:fe:73:17:a7:b0:0a:2a:0d:c4:cd:f4:54:75:9f:71:c1:51", Digest="1yqMPnE79sSMCfqs7HRvnA==", Issuer="fv-az884-957", Subject="fv-az884-957", AlternativeSubjectNames=QMultiMap((QSsl::DnsEntry, "fv-az884-957")), EffectiveDate=QDateTime(2024-02-01 00:19:53.000 UTC Qt::UTC), ExpiryDate=QDateTime(2034-01-29 00:19:53.000 UTC Qt::UTC)) : "Der Name des Hosts ist keiner aus der Liste der für dieses Zertifikat gültigen Hosts" ( "Der Name des Hosts ist keiner aus der Liste der für dieses Zertifikat gültigen Hosts" ) \n \tError in QSslCertificate(Version="3", SerialNumber="28:9d:89:fe:73:17:a7:b0:0a:2a:0d:c4:cd:f4:54:75:9f:71:c1:51", Digest="1yqMPnE79sSMCfqs7HRvnA==", Issuer="fv-az884-957", Subject="fv-az884-957", AlternativeSubjectNames=QMultiMap((QSsl::DnsEntry, "fv-az884-957")), EffectiveDate=QDateTime(2024-02-01 00:19:53.000 UTC Qt::UTC), ExpiryDate=QDateTime(2034-01-29 00:19:53.000 UTC Qt::UTC)) : "Das Zertifikat ist selbstsigniert und daher nicht vertrauenswürdig" ( "Das Zertifikat ist selbstsigniert und daher nicht vertrauenswürdig" ) \n "

But I am wondering about the remarks about the SSL certificates. The same client has no problem to synchronize the Calendar (via Thunderbird) to the same server. And actually I entered the IPv4 adress for the NCP server, no domain name.

And I have several of these line

2025-01-26 20:19:13:207 [ info nextcloud.gui.folder.manager /run/build/nextcloud-client/src/gui/folderman.cpp:1119 ]: Scheduling folder 2 , the last 1 syncs failed , anotherSyncNeeded 0 , last status: Not yet started , time since last sync: 1493710
2025-01-26 20:19:13:207 [ info nextcloud.gui.folder.manager /run/build/nextcloud-client/src/gui/folderman.cpp:708 ]: Schedule folder 2 to sync!

Deleting of the Cache directory
~/.var/app/com.nextcloud.desktopclient.nextcloud/cache/Nextcloud
on the client with a subsequent reboot was also not helping, the client still stucks at “Synchronizing file 0 from 124”

Does anybody has an idea ?