Negative time in live chess?

I wouldn't think the client would be set up to allow negative time. That said, the server keeps the accurate times and what the client shows will update when a move is submitted. If you look at the game in your archive, on the website, you will see what the times actually where.

That's why time can increase after a move has been made: 

https://support.chess.com/customer/en/portal/articles/1444849-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken-

So, maybe a recent update introduced a bug allowing a display of negative time or the site changed how they display it when waiting for the opponent's move .

 Thanks for answer!

That is an indication of latency. If your flag is correct, the traffic from your client to the Chess.com Live servers has to travel through a lot of different hops/pieces of equipment and each hop adds some latency. It doesn't matter how good your local connection is to the internet, since any of those hops can cause connection problems.

https://support.chess.com/customer/en/portal/articles/1444876-what-is-lag-and-what-are-the-colored-lag-indicators-in-live-chess-

If you are on the website, take a look at some of the newer Live options. You might be able to find one that works better for you.

https://www.chess.com/blog/News/how-to-adjust-your-live-chess-connection