ShortPixel says that all images were optimized, yet the old, unoptimized images still appear on the site.

If you used ShortPixel Image Optimizer and optimized all the images on your website, but the old unoptimized versions of the images still show up, do the following steps.

1. First of all, make sure that the new, optimized image, is returned by adding ?something at the end of the image URL. For example: https://shortpixel.com/img/slider/condor-optimized-by-shortpixel.jpg?something
   1. If the optimized image appears, then there is a caching issue (see step #2 below).
   2. If the old, unoptimized image appears, then it is very likely that the image was not optimized and you may need to make sure you optimize it. Go to your Media Library, look for the image, and manually optimize it.
2. Known caching issues: make sure to clear your website’s cache to rule out any issue related to cache. How to clear WordPress cache