The affected images all appear to be ones that were taken from an earlier (Non WordPress) version of our site and imported via a custom PHP script so it could be possible that some database fields might not be correctly set up. Though I think the problem appeared sometime after this was done. I remember that we hit our limit on number of compressions in the month it was done so many of them must have been compressed at the time despite the media library page now saying otherwise. I don’t remember seeing any error messages at the time but this was over 6 months ago so I can’t be 100% sure.
The images are all on the local filesystem, we’re not using Amazon S3 and the filenames use standard English characters.
Very odd things happen if I attempt to reprocess an image.
- Click on a thumbnail in the media library and the usual page comes up with the image and text fields.
- Click on “Edit image, then “Flip horizontally” and “Save” – the image vanishes from the edit page
- Go back to the media library and refresh. The text details for the image are still there but no thumbnail.
- Click on the blank space where the image should be (or on “Edit”) and the Edit page comes up with the text fields but no image. Then click on “Edit image and the flipped image comes up.
- Go back to the media library and refresh, still have the error message and no thumbnail
- Edit the image again and click “Restore image”. The thumbnail for the original unflipped image is back but still the same error message
During all these operations the file in the uploads directory is unchanged. I’ve checked that the uploads directory is writeable by the web server.