I was playing in multiplayer with my friend on the level inside of the Desert temple. After all the moving walls and blades in the floor that damage you, the infamous Arch Illager showed up and our quest became “Survive the ambush” or something, as it does. We killed all the mobs and no more were spawning, but the purple shiny iron bar door thing wouldn’t open. We went back a significant amount and didn’t see any mobs that we had to kill, and if we would have had to go back further than what we did, then I feel like that shouldn’t be required. We waited and nothing else spawned and the door stayed shut. I can’t provide a screenshot because we already closed the game (sorry), but I hope I described it well enough.

Thanks for your help and stay healthy!