Act 2 Boss multiplayer no npc

In a Copper Citadel, me and my friend tried to do the act boss and we both died from an attack the npc is supposed to make dodgable by protecting of the wind.
The npc was stuck behnd the arena door, probably because my friend ran in and i had to take the door behind him.
So we died because of this bug and wasted a citadel that took hours to find.