Mob spawned in wrong area

Doing the Cultist refuge Nightmare Dungeon on WT4. The mission step is to"Slay the Overseer and collect the Cultist Key". The only problem is that the mob has spawned BEHIND the door that the key he drops opens. Can’t get to the mob, can’t aggro him through the door. have tp’d to town and back, nothing solves it, the only option is to abandon the mission.