So been having trouble on this boss (because you guys cant balance summoned creatures so I suck) but anyways last night had no trouble phasing him to phase 3. Today I try this and 5 times during Phase 2 he just stands there and no longer takes damage. Nothing else I can do and now can't play the game. Phase 2 begins with him in like a dark form, then he goes to regular Heimlock form for awhile and all is still ok but once he changes to his Dark form again he just stands there, you can fight away his energy shield but his hp doesn't move any longer and thats it. I play plagueburst, infinity blade, summon archer. New patch clearly broke the fight.

https://www.youtube.com/watch?v=c6r_2p10NEU