Thanks for the update. There’s another ongoing discussion where a user is seeing strange buffering/caching behaviour for the main plugin window here:
I don’t know if the underlying cause is the same, but there’s a possibility the issues are linked.
In the other post, it sounds like the plugin UI sometimes renders incorrectly while the plugin window is being moved around on the screen. Maybe you could ask your user whether the plugin UI changes at all when the plugin window is moved.