I take it you haven't tried directly to the router (you need to actually troubleshoot the issue). Try it it before you move on. Also, do you get an error code?
I was receiving a black screen when trying to watch BT Sport when it first popped onto my EPG about 10 days ago. There was also an error code of IPC6001. A quick google around and the solution was to reset the Youview box in maintenance mode: Link to PDF. I used option 4.
I can confirm that BT sport 1 & 2 SD & HD, ESPN SD & HD, as well as the 18 extra channels are all working on stock Powerline 'Simpler Networks' adapters without issue. I'm on Infinity.