We also only see blank pages for video previews for all Vimeo content.
Currently, open-graph data will be used for thumbnails.
When I try to curl a Vimeo URL for this data, I get a page with a captcha, missing any open-graph data.
Might this be the root cause of not showing thumbnails on some sites?
Is anyone aware of how to authorize access to Vimeo for oneboxing?