Quote Originally Posted by simon1066 View Post
Ok, I think I know the why. Visiting this image in chrome, dev tools shows it as having a type of 'document', it should be 'webp'

HTML Code:
https://www.allmart.ca/store/images/banners/PRIME-Header.webp
Click image for larger version.  Name: Screenshot 2023-05-17 133635.jpg  Views: 422  Size: 29.4 KB  ID: 20296

So you can rule out the slider plugin. I don't have the answer though, possibly server or .htaccess related.
No, Chrome seems to show all images as type Document - so I don't think it's that.