When I was fighting a guy, his timer kept resetting :(


Your recent live games have been 15|10 which means 10 seconds gets added to a player's clock after their moves. So if a player is playing quickly, their time will increase.
Also, lag compensation can cause clock increases and if you're experiencing high lag or disconnects, you may not be receiving the moves in time and when you do, their clock will be set to the correct amount based on the official server clock.
https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken