Every time I save a project on scratch something weird and annoying happens. I can't make a thumbnail. I make my thumbnail and try to save the project with it on screen. With it showing. And this is pretty much the only way to make a thumbnail. But instead of saving it with what I put on screen like usual, It make the screen white, or doesn't even save the screen when i exit to my stuff and look at the project. It happened to my last project. Please fix it.

Try this. it should help with setting a thumbnail.
https://scratch.mit.edu/projects/468866971/

Try saving it as a copy, then saving the copy with the correct thumbnail. That should work.

This happened to me once It's because scratch thinks your thumbnail is inappropriate this happens to some of my projects and others work but with missing features.