Benutzer unerwartet zu Direktnachrichten hinzugefügt

[JammyDodger]

I believe that has been reported and fixed. If you update to Latest it should sort everything out.

Users randomly added to private messages (including messages from System)

That’s this issue Invitation can cause users to be erroneously and transparently added to private message · Advisory · discourse/discourse · GitHub It has been addressed in version 2.9.0 beta 12 which has been released earlier today, so upgrading would resolve this. The update also contains code that removes the users from the PM’s again.