After 20 minutes of playing, during the first quest in the tutorial, when attacking the bandits camp with my brother and the headvillage troops, I failed while fighting the enemy chief in a duel.
So I was knocked down and the quest told me to try again the camp assault. Instead of that I talked to my brother in the party report, and the dialog that popped out was him telling me about a chest he found after sacking the camp and blah blah.
So the game was behaving in this dialog like if I would have been successful in the camp assault, when I actually wasn't.