https://support.chess.com/customer/en/portal/articles/1444849-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken-
I know that the amount of lag forgiveness has changed fairly recently (month ago maybe) so if you hadn't noticed it so much before, that could account for what you are seeing now.
edit: guess it was at the end of April; under Live Chess https://www.chess.com/blog/News/chess-com-dev-update-april-28-2017
Has anyone experienced an opponents last few seconds of time constantly increasing when in final stages of losing the game.
George First.