Uncaught ReferenceError: ytcfg is not defined (also __ytRIL is not defined)

It looks like the bug is on youtube's side. You can see the same JS error here: https://www.youtube.com/embed/U-xetxYwyak

This is a Google bug. It also happens on Youtube's developer page. https://developers.google.com/youtube/youtube_subscribe_button

The following bugs tracks this issue.

https://code.google.com/p/gdata-issues/issues/detail?id=8569 (Still active -as of Jan 5h 2017)

Please up vote on this bug using the links below so that it gets their attention. They have been sitting on it since Sep 9, 2016!!.

This started happening even on youtube.com when you click the "Share" button under any video and then the "Embed" tab to copy paste the embedding html code. Definitely their fault.