Followers in the dregs get lost and stuck in the dungeon somewhere. They show in the map as in the dregs but they dont follow out. Having another thrall follow so they scout allows them to come home.
Steps on how to reproduce issue:
Goto dregs with thrall
thrall becomes lost
have another thrall follow so original thrall scouts
I was in the dregs also, my thrall was not much use tbh, he got stuck a few times. Then spent pretty much the whole end fight in the acid pit and did not help at all. He came out all happy and unharmed once I killed the worm.