I've actually been having this problem aswell. I ran into it questing in Northrend. From what i can tell it is running into caves or buildings to complete quest objectives and will find its way in fine but goes into an endless load tiles loop when i tries to navigate out. Only workaround i've currently found is to manually move the toon into a more open area (outside) and then stop/restart the bot and it will continue until the next cave or building. Oddly i have not had these issues anywhere accept northrend.