Time Added to Opponent's Clock


This support article explains most likely why the jumps occur:
https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken
Of course, I always encourage taking steps to help minimize your lag - especially if you are playing blitz categories: https://support.chess.com/article/213-how-do-i-fix-my-disconnect-