I'm still pretty new to D4 and had the difficulty set too high when I tried to kill the butcher for "A Taste of Power" quests. When I go back in, the butcher doesn't respawn. I've tried restarting my game, changing difficulty, resetting dungeons, etc.

I saw something recommend trying to join somebody else while they are completing it for the first time. Can I jump in with somebody or does anybody know how to fix this?