When you pull the first two mobs out of AoW area (the two above, right inside the door), they sometimes will sink under the floor (has happened twice to me) they then hit you while half under the floor where you can't see them to strike back. I've experimented with damaging them or just agroing them, in both cases it can happen.
Its annoying to be killed by these mobs on the way to tank AoW or at least delayed by messing pathing. I went FD once when half under and then /q eq. Came back on the roof of the building where AoW is found !?.