There were an update recently which included a bug with resignation (but has now been fixed). Checkmating a colored dead king was another thing they added. You can get updates and find the changelog in the club:
https://www.chess.com/club/4-player-chess
My opponent resigned to claim win and I got 0 points for him resigning and finished last
Also saw a dead king "check mated" not taken for 20 points????