More players in a challenge than in the party, causing game error. 305594340

I've been playing this wonderful game for two days now but I have the same problem as you. As much as I have tried to play in a group, when the mission ends and I want to collect my reward, I am automatically kicked out of the game with the error code: 305594340. It's completely frustrating since I also have to follow the story mode and I can't advance because it also asks me to form a group and I always get the error at the end of the mission.