Vimeo cover image became wrong
Vimeo just updated its code, which made all its previously used thumbnails/cover images to not work anymore. At the old thumbnail links, now only this image displays:
To resolve this problem, you should go to your Vimeo layers, remove the "Vimeo URL Or Video ID", click next to its field, then put it back. This will regenerate the Vimeo api given image, which should be fine.