Thrall disappearing

Game mode: Online
Problem: Bug
Region: [Here]

Steps on how to reproduce issue:
1.Placed 2 archer thralls on a wall
2.Logged off for a few hours and when I came back the archers were gone. Nothing on the event log
3.Placed a named fighter thrall in front of the keep
4.Logged out for a few hours, and when i came back the fighter was gone. Nothing on the event log.

My keep is in a very hard to get location, and since nothing is on the event log, I know they were not killed. I killed a thrall myself to make sure the event log was working and it is.

This seems to happen to only to thrall that do not have a cover of some kind over them. 1 Archer and Dancers I had inside a room are still there.