Since Statically using multi-CDN, not all CDNs support dynamic WebP, Cloudflare for example, only generates WebP after the image has been cached and smaller than the original. Because there’s no reason to convert an image to a different format if it ends up just getting big and slow to load. Practically, this shouldn’t reduce your website performance.
However, this is the challenge of running an auto-WebP service on multi-CDN. You can learn more at https://support.cloudflare.com/hc/en-us/articles/360000607372-Using-Cloudflare-Polish-to-compress-images