Single-player: No Mods
In a little hut, outside of New Asgarath’s walls, on the cliffside in the southeastern corner - NPCs get stuck in the door… always.
(This time it was three, other times two - once there was only one NPC - yet he still got stuck.)
They can never pass the doorway.
note: As you go into the main gate of New Asgarath, to the left is a hut that you cannot go into.
(There is no door blocking entrance - door frame is too low - yet the one on the right you can enter.)
Speaking of which… should you not be able to open the door on the tower behind these huts?