I got stuck in loading screen while on queue on Mission. Closed TOS and re-logged. I tried Re-entering Auto-Matchmaking and this happened. 6 man party and I’m way above their level lol. Boss level is 197 and they kept on dying cause of very high level gap. Others ended up leaving the dungeon and sadly after killing it, no experience give to me 
instance mismatch isn’t new, happened before and never fixed