I have restated my game, hard reset my internet, hard rest my xbox, and in an extreme measure yesterday, I bought the season pass and downloaded that new map to see if that would fix it.
I can't find anything about this exact problem anywhere and wondering if anyone has had this problem and fixed it.
I have tried this a few dozen times over 3 weeks with 7 DIFFERENT people and I just keep getting the same result. We will be in a party and we will be partners, and every time either I or my friend try's to load up a mission and either Him or I join in to play it, after about roughly 10 seconds, my friend with crash and be dashboarded but I'll be fine and I'll get a message saying that my partner has disconnected. So since this game came out, I have been unable to play those co-op missions with my friends.