I have been playing with a 4 man team through the main story campaign and we noticed 2 game breaking bugs. The first bug is if one of your characters dies you don't get a chance to revive them because the game instantly ends. The second game breaking bug is bosses with legendary actions just break all the time. They either do their legendary action or just fight normally without them not both. This made it hard to play.
Some inconvenient bugs are if you tab out or do an action that only the main character should be doing it desyncs the PC and makes some imaginary items that don't actually exist on the other players that disappear on reload.
Until it’s fixed (and I hope they do), stay away from the Swamp in multiplayer. It’s unplayable. Every fight gets de synced. Everywhere else seems OK so far. We have a crash or 2 per session but the swamp is impossible.
Please restart the Australia server - it's started to lag several days ago and in "waiting for a player" spam state when the game is started (no such issue on some other servers)