Owncloud Windows: lost a whole album sync and can't re-add it

Hello

Updated:
I checked the cfg.backup and the 27 10 2023 it created a backup file when updating from 3.2.1 to 5.0.0.12278: this is the moment where ALL the mentions to the 0\Folders\2\ disappeared
But that’s weird because in the .owncloudsync.log of that folder, I get sync messages from this week
#=#=#=#=# Propagation starts 2023-11-12T21:30:08Z (last step: 230 msec , total: 230 msec)
#=#=#=# Syncrun finished 2023-11-12T21:30:08Z (last step: 12 msec , total: 242 msec)

At boot I saw that one sync folder is missing in the list.
I try to re add the folder and then I got the message “is used in a folder sync connection” So it knows it has been synchronizing that folder
On the server everything is fine

It also asks me to update to 5.1.2.12600 ; I do that but the missing folder is still not there and I still can’t add it again.

no log in the folder ownCloud-logdir

How can I safely recover the synchronization of that folder please?

Thank you