DT will not quit, saying "Schließe Synchronisierung ab..." which never occurs, only force quit possible

After updating to 3.8.3 I can close DT only by force quit. Normal quit will produce the notification “completing syncronization” (in german, don’t know the original message text in english) in the activity window that lasts at least four hours or longer - never saw it actually quit after that, because I force quit it every time)

Quitting a second time is sufficient. In addition, what kind of sync locations do you use?

Hi, sync location is a own WebDAV-server on a Synology-NAS. This behavoir has become less frequent in last weeks, but syncing remains to be very slow and appears to be stuck in a loop. Whenever syncing is finished it startes again (with the same slow speed and same no of files to be synced).
This is true only for two databases which are also affected by the missing manifest error, described here: /t/problems-with-cloudkit-sync/70170

This is a known rare issue which will be fixed by the upcoming maintenance release. Quitting a second time is sufficient.