I don't think the answer is complete. And without School doing what ? They are always intended to follow the Main School... What else should do ?
Let me guess... something like flies are doing - tracking a random spot in water and swimming there ? Circling in area ? Crawling around original location ?
UE Editor Note
If "Level Validate" would be operational, one of checks which could be added is exactly removing all these junks out and logging them correctly. Perhaps this is what will do MapGarbage without discrimination - these are not mapping actors and weren't supposed to be mapping actors.