Public Vimeo oneboxes regressed in this commit. It looks like Vimeo doesn’t add og:video_url metadata in public videos but does so in private videos, very odd.
I fixed this by defaulting to oEmbed for public videos and using dedicated engine for private videos only (where we need to sprinkle magic attributes).
https://github.com/discourse/onebox/commit/c43ba86f995f924ce61cae411ad9ed052319c310
Thanks for reporting this isssue @Richie. 