Why some of the images and/or thumbnails cannot be optimized?
Sometimes, after running Bulk ShortPixel there are still some images and/or thumbnails that aren't optimized.
Usually the causes for this are:
- the actual images are listed in Media Library (or database) but they do not actually exist on disk anymore. A quick solution to this problem is to use a plugin like Enable Media Replace to replace the missing images with new ones. Then ShortPixel should automatically detect the new image and optimize it along with its thumbnails.
- the images exist on disk but they are not accessible from browser. This usually happens when a website has been recently moved from one hosting provider to another. The solution is to change the permissions for all the files to match the files owner needed on the new hosting provider. Usually this can be done easily by your hosting provider.
- the thumbnails used to exist in the past or the thumbnail sizes are defined in WP settings but they do not exist on disk. They usually aren't needed anymore anyway as they were needed, for example, by an older theme employed by the website, a theme that isn't used anymore. The solution to this kind of problem is to usually just ignore it.