I also have the same issue with built in Intel UHD 620 graphics after updating to 1.9.1-30ef802f. Unfortunately it makes Mailspring next to unuseable at the moment.
I don’t have the issue with any other electron apps.
Resizing the window doesn’t always cause the window to repaint and often quit is required.
--disable-gpu flag doesn’t resolve the issue but it seems like it makes the repaint on resize always work.
I could be wrong but it might be something to do with lack of RAM, I have some other electron based apps that go to a background colour and title bar state when I haven’t used them in a while and when they get re-opened, they need to essentially re-load. They look the same as Mailspring but Mailspring doesn’t handle the reload.