I was just doing the Dungeon with my friends, it is not my first completion, however when i died this time it sent me back far enough to where the previous secret chest is. On my attempt to re-join my friends, i then got hit with a turn back zone. There was no way to return to my friends, i had to leave the dungeon and return in order to get back into the boss room. Not too horrible unless you're trying to complete dungeon triumphs.