Earlier in Wayland adoption I recall some found that using the same Refresh Rate helped with a few multiple monitor configurations, at least with scaling and resolution issues.
That’s clearly nothing to do with the current problem, of course, but it might be a useful note to file away. 
There was a similar issue on Mac hardware in one or two topics only recently (within the past month or two). I’m afraid I don’t recall the topic titles, but a careful forum search might reveal them (both were “Mac 11” from memory, so that might be a place to start).
I think ideally it should all have been lowercase, but no matter; it’s rare that the caching issue arises; but it does happen.
It’s possible Chromium is the common denominator. There have been one or two complaining of random screen artefacts since the update.
They didn’t specify exactly what was affected (Plasma was mentioned but it might be something deeper), in fact, they didn’t give a lot of information at all, but it may be a direction to follow.
These were only a few after-thoughts.
I’ll chime in again if I discover anything with any substance.
Regards.