Default [Q] Youtube won't go into full screen

Hey guys, I don't know if this is in the right category so I apologize if its not. I've been having this problem with YouTube on my HTC One M8 where the Softkeys and Nav bar still show in a video from time to time and won't go completely full screen, I am rooted with no Roms or Kernals and have S-Off but I doubt that makes any difference. I do have Softkeyz but if this was the problem wouldn't it always be like that instead of sometimes? Has anyone any idea what this is or how to fix it?

This is what its like -