Welcome to this user forum.
I assume you have purchased the multiroom (2 YouView boxes) option?
With two boxes it would be best to have a direct Ethernet to both, to ensure that the full bandwidth is avalable.
Test it first with a direct cable.
Which type of powerline adapters are you using, and how many are slaved from the master one connected to the home hub?
Remember, you must never connect more than one powerline adapter to the home hub, that is the master one, all others must be slaved of that master one, otherwise you will crash the home hub.
Here is an explanation Important - Using powerline adapters or broadband extenders
How do you propose to connect the PC in another room?