Wow, what a coincidence! I was about a 7 or 10 days behind the latest commits. I just updated, and all of the new images I’ve tested seem to work:
https://www.gstatic.com/webp/gallery/4.sm.webp
https://filesamples.com/samples/image/webp/sample1.webp
https://www.gstatic.com/webp/gallery/1.sm.webp
However the URLs that I tried previously seem to be cached or something, because they’re still giving the same error.