Actually the wrong code is present in all resolutions. Hard to check what might be causing this issue when Webp Express is Active and without access to your backend, I cannot switch it off to compare. So instead of using:
- Replace <img> tags with <picture> tags, adding the webp to srcset.?
- Dynamically load picturefill.js on older browsers?
Try selecting the next option instead:
- Replace image URLs?
- Only do the replacements in webp enabled browsers
And experiment with
- Use content filtering hooks (the_content, the_excerpt, etc)
- The complete page (using output buffering)
To see which option works for you. This should hopefully help resolve the issue. Also, no way to know if you are using any caching mechanism and what options might be active there but if you do make sure at the very top of the settings page of Webp Express you use
Operation mode: CDN Friendly
Hopefully that helps!
