Error code “Non-existent changeset UUID.”

Hi everyone, I did a search on UUID and found no help/support topic so PERHAPS I BUSTED THE BUILD! ??

I’m only getting this when I visit Dashboard > Customize

I have been trying to customize a CSS element.

I’m running a Customize Twenty Seventeen BoldThemes plugin and another called Easy Google Fonts that I might not need; I also ran a Custom CSS & JS plugin which I have just deleted my CSS attempts and deactivated. This has not fixed the UUID error code.
I have a few other plugins running but not too many.

Does anyone know what I might have done, and how I can fix this? I’d like to get it back, and use the regular Additional CSS editor to try a thing.