https://support.chess.com/customer/en/portal/articles/1444849-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken-
It's also possible you got disconnected and when the client reconnected the time was corrected to take into account that fact.
What ever u play well
on my phone I was waiting for my opponent to move for 15 minutes just to go on a web-site and realize that he actually made a move and it was my phone app that [no need for exlpletives -- MOD] up the game and made me lose by time. Conclusion: play via browser
it is so weird. the app gave extra time to my opponents and now I receive this message about fair game policy. wtf!