@Avron:
My radicale also has hick-ups, had to create 2 new calendars, error 500. That is surely a different topic. (This happend prior to the upgrade, about 2-3 weeks ago).
And also Syncthing is not running, since 4-6 weeks, I guess. Hope this resolves with the upgrade.
PS: see my EDIT2 in the first post with the broken file. That might be the cause of the failing upgrade.