CDN URL Mapping not working on Source srcset

Let’s take the code below as a example.
<img src= value has been modified to point to the cdn as expected.
<source srcset= value is not modified.

So it seems like CDN mapping only works for img tags and not source tag within <picture>

Is there any solution for this ?

<picture>
    <source srcset="https://www.925silverjewelry.com/wp-content/uploads/2018/11/Swarovski-Capri-Blue.webp" type="image/webp">
    <img src="//cdn.925silverjewelry.com/wp-content/uploads/2018/11/Swarovski-Capri-Blue.jpg" alt="Wholesale Silver Paw Print Stud Earrings" title="Wholesale Silver Paw Print Stud Earrings" class="webpexpress-processed">
</picture>

The page I need help with: [log in to see the link]