It seems the YouTube iframe API is broken or undocumented changes have been made. Even the example from the documentation does not work correctly. onYouTubeIframeAPIReady() is not called and manually triggering the stopVideo() function throws an error on their example.
Calling the stopVideo function from their example produces the following error:
TypeError: Object #<T> has no method 'stopVideo'
Also noticed loadVideoById() no longer works either.