The updates went fine, all clients are now running version 18.104.22.1686.
Don't get me wrong, as the IT-Admin this isn't a huge problem for me, if the icon isn't there. It'll be there after the next restart / power cycle.
Now, a few minutes after the update the first clients are running their scheduled backup at lock-event. Hail to the smoking break with the colleagues
So it's not a huge bug at all, it's not breaking the schedule, the functionality or something else. Its just the setup routine running in silent mode which is not starting the tray icon again.