For anyone who is struggling, and really wants to progress the story. DO NOT USE SUMMONS, try bone spear (or spirit if you have the gear) necro!!! Do your absolute best to stay within the center ring (the one that surrounds the triangle graphic on the ground), and DO NOT be outside of that circle when he casts his teleport. If you are on the outside of the room he will teleport outside the ring and bug out. You can clear it by staying in the center of the room, with no summons or minions. It sucks that blizzard refuses to fix this but YOU CAN DO IT!!!