I’ve had a thrall get stuck in the volcano twice: Not on any rock or stair or bridge, just right out in the open on a path they stop dead. If they follow me out of the volcano then they are stuck at the entrance. The only way that worked to get them back to base is to take all of their gear away, have them un-follow and then use the Rescue feature. This brings them back to the base where they start running away as if going somewhere (like back to where the bug started) regardless if I put them in a spot and have them guard.
This is on a private server vanilla game PVE with no mods whatsoever.
This is game breaking Funcom.