Well that's quite an issue .
But I quite didn't get which game was deleted off the screen . Did the new game with a new opponent get deleted ? Or the accepted rematch with the old opponent get deleted ?
If it's the rematch that got deleted , here's a small fix that I can suggest. Quickly open a new window (before you lose due to abandonment ) , and go to your games archive . You should have the latest match , with the opponent you rematched at the top of the list . Click on his/her name and go to their profile . Since your game against them is still ongoing , the Watch button (in red) should appear instead of the regular challenge (in green) button on their profile . Click on that , and it should take you to the game . And you can continue playing .
However if it's the new game with the new opponent being deleted, I am not sure how to deal with it .
Sometimes after a blitz game, I click on both rematch and new game. Then, the new game gets accepted, and I play a move. Then, my opponent accepts my rematch, and a new game starts.
Back when we had live chess instead of Play, you could just tab the games. But in play, if a new game starts while you're already playing one, it just deletes the old game from your screen completely, so you can't move and you can't do anything about it. Then, because you've already moved, you lose the game by abandonment and probably get your account auto-flagged for bad sportsmanship.
Here's a game where I lost because of this: https://www.chess.com/game/live/136023928918?move=0
I also lost another game due to this a few days ago, but I'm a bit too lazy to go digging for it.
I've turned the "Play multiple games" option off in settings now, but if it's there, it should work properly. It might have been wonky ever since leagues were implemented, but somehow I've just never had this issue since that point in time until now.