Many of the new bosses have Hard % damage caps on how much damage they take. Apparently this is intentional. This really.... really shouldn't exist. What is the point of working on new equipment or damage if I am hitting these caps. It makes me less motivated to play or spend on this game.
I heard the director confirmed this exists and this must be what is cause certain mobs to stop taking damage when they shouldn't. Seeing hp bars suddenly spike back up when you deal a crit makes the new crit % set effects essentially wortheless and red upgrades worheless.
I understand some bosses need phases, just make separate health thresh hold meters for this. Where the phase is required. Thats it.