Just certain images or all? Did you check with another image? We have seen issues with corrupt meta data embedded before. If you can link to an image directly (here or on a ticket) so we can try with on of yours.

I just opened two tickets on GitHub which I believe are related to these issues.

It only goes through if you edit one image at a time, doesn't work if you want change multiple images.

I still strongely suspect that is the form element limit on your server I talked about. Though there should be errors about that. Have you tried setting it to 5 images per page?

So the "edit all images button" should now work from all image edit pages. Also I moved the tag selector to the single image page only. Please try if that solves the speed issues as a quick fix.

I finally could reproduce the bad image uffix error but I have no fix yet. That might take longer to fix.