James on 16 Oct, 2015 08:11 AM
Have you tried another video?
I think you may only experience the problem with videos that do
not allow to be embedded.
Currently Apple have a bug with WebKit that does not allow
fullscreen YouTube videos to work. We found a work around via
embedding videos. However if a video uploader has disabled the
ability to embed the video then it can not go into fullscreen.
As soon as Apple fix the bug it will be fixed. Also note all
other apps on the App store do not have fullscreen working at all