Clock re-timing itself over and over after reaching 20 seconds to go!

Is this a cheat, as in my last game, that some computer 'know hows' have worked out or been shown?

The clock reset happened over and over again, at least half a dozen times. Can anyone shine a light on this please?

It's likely that your opponent starts playing fast when one or both clocks get low, and if you have lag, then it will appear the clock is jumping around, especially if your opponent is premoving.

Thanks llama, I hope it was that... yet this went on for several minutes, jumping from 19 seconds back up repetitively.

It's a common question people ask on the forums.

https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken

I have always believed it is chess.com's way of rigging games to favor those who pay for premium memberships where you get lessons, study plans and so on as opposed to those who teach themselves how to play and end up winning on time a lot.

Obviously Yoyostrng, you would win this game on time if it were a fair game, but mrpoopyhead4000 who gives us $2000 a month is performing his Sicilian Turbo charged kings dragon gambit with a French open denied which he learned from our lesson plan, so the clock seems to be malfunctioning in his favor. Eww...

If they wanted to use that to sell memberships, then they'd be stupid to not advertise it.

Since they don't advertise it (and since it doesn't make much sense e.g. driving users to competitor's sites) your idea isn't very believable.

I edited my post after you commented to further explain.