Sept 5th Duckypb opened a very similar support ticket.
Pasted is an image of my library with the blank spaces. It happened yesterday afternoon as I was working on my site.and working on the add feature image section.
I deactivated all plug ins and there we no changes. I deleted the images, cleared cache and tried to upload different images all with the same blank result.
I went to my dev site and uploaded and the issue was not replicated. I flipped back to an old theme and all appeared ok.
If I attempt to click on the image and force add it as the featured image. NG