File sync errors in endless loop

Hi all,
Sorry for the screenshot with messages in Czech language, it says “upload was not successfull - file not found”.

It’s stuck in a loop (with up and down changing number of files to do) for whole week now.
I have dissmissed hundreds of the messages already.
If the phone is restarted, the line of unsuccessfull uploads starts again after opening the app.

I don’t know how to cancel it, but most importantly I don’t know how to debug it.

Windows and linux clients are syncing files from the same nextcloud account succesfully.

I checked the permissions and everything seems set up properly, at least at the surface level normal phone user can see.

Thanks for any help.