Rook's Nest Boss - Bael Bug?

Anyone tried to fight Bael in rook's nest and meet this situation? Bael just stand and doing all those lightning charge, then we can't hurt him. This happen on normal map and the elite Rook's nest as well. Me and my friend keep attacking Bael but we can't hurt him, this takes like 30 minutes and nothing happen.

P.S Bael in Rook's Nest - Elite is wicked, his hp is insane. Took us like 1 hour to kill him lol

heres what we do.

if he froze you must go to a distance were u and your pet cant attack him. Then wait til he moves back.


tried and tested.

I have even tried to leave the game and join back. Failed.

Anyway I had finished killing Bael Elite map, and I didn't get the achievement.