have also had this issue, tend to find theres a 50/50 chance whether closing the game will cause it to count the round as not happening or having been successful if i managed to extract. i let it stay open for a few minutes to see what the server would say and ended up with
has happened several times with no specific rhyme or reason, doesnt happen often but is annoying when it does. from what i can tell the pause interface is still active beneath the black screen and using it to dc the lobby just leads it to get stuck in lobby with the ambience still playing, even long after the raid should be over