For whatever reason, databases become corrupted.
In Windows File Explorer, the thumbnails displayed are a convenient link to files you've been working on, recently. When the database becomes corrupted, these pictures display incorrectly.
Hankers forwarded me the link to this article on Windows Central which describes 3 ways to fix the problem and recreate the information using the Disk Cleanup legacy tool and Command Prompt.
Not going to scrape the article (linked above) which is easy to follow, and which is replete with screenies and simple instructions.
So, if you're having problems, or keep bookmarks to fixes, Hankers has fixed us up with a good one here. Thanks, Hank.
Have a great weekend, folks.