I like this app but I believe that cheating is frequent in tournaments.


No.
You are probably experiencing lag adjustments.
https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken
No.
You are probably experiencing lag adjustments.
https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken