Previews not created

Very strangely previews were not created for 3 images that I imported today. Other files, including images, were processed correctly. There’s enough space on the server, the files are of regular size…
Did someone encounter such problem?

Were the images of a different format than the others, maybe? Do the same images consistently not work if you try to upload them again?

If it’s the same images and they’re consistently a problem, you could share them here (if that’s permissible) and we could see if there’s something interesting/special/problematic about them.