customized WP medium not showing in frntend

Hi. Love your plugin and many thanks for it.

I altered the WP medium to be 320W.
I select this size for images on a lander (Elementor Pro landing page, or pages built with Elementor). All looks good in the editor.

I cache with WP CloudFlare super page cache plugin
and use Converter for Media for WebP and AVIF.
And CloudFlare. With or without Rocket Loader activated same result.

I can see in the caching plugin HTML fallback the correct size for images. However, on the frontend when I check in Dev Tools and source I see the full large image NOT the medium sized one I selected.

Any ideas how to fix this?

Thank you in advance.