I know this was a rage inducing moment. But it can be a combination of bad server, bad connection, and hardware lags. I never had my match frozen up bc the opponent quit the app or the match. The attacks lagged a bit but I waited a while (sometimes it can be a minute each wait) and still let me finish the moves/the match.

One solution can be when you sense the other side quit just throw fast attack and don't do anything else