Some (a lot, but not all) uploaded images no longer showing in back-end

I have not updated my website in a few months. I signed on to my WP-admin today and for some reason, a whole lot of my uploaded images are not showing up in the back-end. The thumbnails and any previews show up with a little broken image file icon or just the image file icon (without a “break” or “rip” in the graphic). HOWEVER, the published page shows the images just fine.

???!!!