Hello @19ash82,
From what I can see, this is a caching issue. It looks like you are using Cloudflare and on the WebP link you shared the older version of the WebP was cached (with glossy compression if I understood right). If you check this link (I added ?no-cache at the end of the URL to disable the CF cache), it has 68Kb, so smaller than the jpg:
https://www.lesfousdisent.com/wp-content/uploads/2023/09/Main-Coffret-bieres-v2.jpg.webp?no-cache
As a general idea, our plugin has a mechanism that checks the file sizes and if the resulting WebP would be bigger in size than the compressed image, it will simply remove it, because it doesn’t make sense to serve a bigger image, just to have it in WebP format. Such cases are rare, but they do happen.
Moving forward, to get this fully resolved, I recommend you to enable the Cloudflare integration that we have in our plugin, this would clear the CF cache for all the images that are optimized/re-optimized or restored from backup. More details about it here:
https://shortpixel.com/knowledge-base/article/325-using-shortpixel-image-optimizer-with-cloudflare-api-token
Please tell me if you have any other questions!