In the arena in Fort Joy, when playing in multiplayer, me and my friends have had a consistent glitch occur where upon beating the enemies, combat will not end until everyone is dead. As in, until one party has killed everyone, and then proceeds to kill themselves. This leads to certain characters glitching the arena to a point where they have no means of killing themselves (such as our ranger), effectively ending the game. I don't have a savegame of it happening, but it's easy to reproduce - just play the game in multiplayer and do the arena. Furthermore, after the arena is done, you can become "The One" by challenging another player, but this can only be done once, leading to much frustration when I wanted to challenge my friends afterwards, as I had saved over our only save.
