Accend into Madness bug!
You need to wait until your instance reset to join someone else instance.
I’m only responsible for what I say, not for what you understand.
And what does “waiting for my instance to reset” entail exactly? I went in alone at first, then left the area. I tried to go in with a few guildies, it sent me back to the dungeon alone, with the King exactly where I left him.