YouTube preview stopped working (204 error code)

Smth strange happend. All the links from youtube are not previewed.

Only this error in the lightbox:
Sorry, we were unable to generate a preview for this web page, because the web server returned an error code of 204. Instead of a preview, only a link will appear in your post.

Not working in the safe-mode too.

Couldn’t find any examples on meta. Does anybody know what does it mean and how to solve it?