I think he's pretty bugged when it's the enemies are moving against each other event. You can't get his shield down. I've seen people talking about it on the forums / other websites. It took two of us to kill him after a warsat event yesterday. Arc damage and he's easy to kill once his shield is down. Like, stupidly easy. It's just getting the shield down. I had a merry dance with him and introduced him to my blade.