server steals time. from 5 to 10 to 20 seconds + these days

The server keeps stealing time while waiting for the opponent to make their move, even when I’ve made a premove.

It used to only be a second here and there, but now it’s several seconds at a minimum.

Sounds like you're have connection issues and/or high lag.

https://support.chess.com/article/4720-online-chess-performance-optimizations

https://support.chess.com/article/213-how-do-i-fix-my-disconnect-lag-issues

Your servers are the issue. You either can’t maintain connections properly, using bad ping rate compensation(which shouldn’t be used at all), not making proper use of a keep alive, or there is an exploit.
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 If there is an exploit it could be:
-excessive moves on one end causing DOS in the session
-disconnect/reconnect causing timing glitch with ping rate compensation

-or a malformed/fuzzed request which can send requests to adjust the clock. The clock was made available to key users, and then suddenly this became an issue, so it’s likely not to be a coincidence.
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I am not the only one to experience this issue. Some players are constantly winning by time disproportionately. Tracking user behaviour and timing, among other variables, could easily detect the statistical recurrence, and identify outliers.
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I have a 1GBPS connection, and realtime gaming on other platforms works fine, so no, it’s not me.

today I lost 20+ seconds in several games I would have won. Great servers you have there.