It worked for me. Unchecking the check box inserts rel=0 into the embed code after the video url. So you should have youtube.com/embed/yourvideourl?rel=0 Double check your embed code. If it’s not there. Add it.
You can get rid of that over on the YouTube side of things. When you hit embed, before you copy the code there should be a check box below that you can untick to get rid of the suggested videos at the end.
Yeah, mine too. It seems it no longer stretches the page, but is now fixed width. On the bright side, shortcodes seem to work now. Hopefully we can get a fix for this new issue shortly.