While I don’t recommend editing a plugins files, if you need a quick fix before an update to the plugin rolls out, I seem to have tracked down the issue.
In shortcode.php on line 13 if you change
str_replace('https://player.vimeo.com/video', 'https://vimeo.com', $removeoembed);
to
str_replace('//player.vimeo.com/video', 'https://vimeo.com', $removeoembed);
Vimeo videos begin to work again.
My guess is the way Vimeo oembed works changed in WordPress core, but I didn’t look too hard into it.
