The boss leaves the boss's room during the battle

I was playing the special endgame map Sacred Reservoir and fighting the boss Zahmir, the Blade Sovereign. While switching skill casts, the boss disappeared from the boss room, and I couldn't find it. I was trapped inside the boss's room and couldn't get out. I don't do everything, and I also can not continue the battle

Same thing happened to me https://www.pathofexile.com/forum/view-thread/3894561