Some files not synchronized (Client: 5.3.1.14018, Server 10.15.3.0). WindowsError: -7ff8fe88

Some files (suffix jar) are not synchronized on Windows 11 using Client: 5.3.1.14018 with Server 10.15.3.0. on Ubuntu.
I created a owncloud-Log from the client. I found the following message:
status OCC::SyncFileStatus::StatusError : “WindowsError: -7ff8fe88: Die Datei ist keine Clouddatei.”
The files are listed on the tab “not synchronized” (Nicht synchronisiert).
“The server responded with 500 Internal Server error”. The files were blacklisted. (“zur schwarzen Liste hinzugefügt”),

What is so strange is that the same files were synchronized a few weeks ago without error.

All files which are not synchronized are all jar-files.

Thank you very much for your help.

Best regards
Markus