Iron Citadel Boss 1 shot bug

Dropped bosses health to 1HP before phase 2. He charged a wall, swung his sword and 1 shotted me, dealing 10kdmg total to myself, and other party member, who were not in range of the sword swing. At lvl 96, the XP loss is a painful hit. I have a clip of the death.

I’ve encountered this bug with three consecutive Iron Citadel bosses, exactly as you described. I’m playing a bleed build, and just like you mentioned, after reducing the boss’s HP to 1, he one-shots my character with a single swing despite having 9k EHP. I was left wondering how I could die to that attack when I can tank most T4 pinnacle boss abilities.