illegal server
No it's not an illegal server, you had a mini disconnect.
Disconnects and lag: Read these from the Moderator: VintagePawn:
You can do some things to decrease the possibility of disconnects and lag on your side:
https://support.chess.com/customer/en/portal/articles/1444918-my-internet-connection-is-fine---why-am-i-getting-disconnects-
https://www.chess.com/blog/News/how-to-adjust-your-live-chess-connection
Related articles which you may find helpful:
https://support.chess.com/customer/en/portal/articles/1444849-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken-
Articles found in Live Chess:
https://support.chess.com/customer/en/portal/topics/620381-live-chess/articles
https://support.chess.com/customer/en/portal/articles/1444971-how-do-i-fix-slowness-in-live-chess-