Blood priest boss infinite healing

At the end of the doryani interlude, after i kill the blood priestess, the other boss just keeps draining blood out of her again and again, dozens of times, always healing an amount that is way too high to ever kill, im totally stuck. Clearly, "outdps the heal" cant be the answer. In fact i have seen kill videos where he doesnt use the ability in literal minutes, but i dont even get a window to attack before he heals again. Anyone else have this experience? I tried making a new instance and on multiple days but no change

I second this issue. This fight is way too dificult for most clases. This will stop "avg" players from wanting to play or even try endgame. I have over 1000 hours and i wont be playing till i see they nerfed this fight.