zalmarath error de jefe

hace un rato jugando con un amigo, llegados a quitarle 1/4 de la vida al jefe se vuelve intargeteable(no recibe ningún tipo de daño) y se queda así durante toda la pelea, solo nos suicidamos e intentamos de nuevo, pero el problema persiste.

Somehow stuck on the spanish forum... not sure why. After Google Translating, I believe I'm experiencing the same error. I was able to damage him past 1/4 health one time I think, I think it has to do with him moving around the arena causing him to become invincible sometimes. Playing as a witch, my auras or curses don't affect him either when he's invincible. The arena overall seems to be buggy, as my camera will jump up and down a lot when I'm near the areas he broke and I've crashed multiple times during his swipes/arena breaking.