Lost folder after unchecking in sync client
A client lost a local folder, which was in the sync tree and has been unchecked. Well, if you uncheck a folder you get a warning and need to confirm
However it seems that the folder was not deleted immediately, but 4 months later after a total re-scan that was triggered after a server migration. So the client assumed, that the folder inside the sync tree does not get deleted and he could manually switch on and off server syncing. Now an outlook pst file is completely lost which is not amusing.
The only reason that this could happen according to the discussion in https://github.com/nextcloud/desktop/issues/1238 would be that a folder is being moved into the sync folder and then immediately stopped from syncing, while not having been uploaded yet.