There are a xouple of things that can be happening.
1. You got disconnected from the Live server. That can be caused by a number of things. Some you can look at on your end (for the web client anyway). In a mobile device, having the strongest signal possible is advisable.
https://support.chess.com/customer/en/portal/articles/1444918-my-internet-connection-is-fine---why-am-i-getting-disconnects-
I know recently the site has experience some load issues causing some Live disconnects (posts by staff). Not sure if that has been resolved or not.
2. You could be seeing clock adjustments due to short disconnects and/or lag compensation.
Thank You,
JKing