Watch Rerfus:

That's the spawn point.. Once the mob gets to about here:

It falls under the floor of the top area, and you end up with 2-3 Adds and possiably a dead Cleric:

My suggestion if possible, would be to path those spawn points to the center of the door first (One of the right Paths Left to the center of the door then comes straight toward the player, One on the left does the same thing). As it stands now they do a diagonal straight toward the player causing them to get caught on the pillar and falling into the floor.