How is the X box 1 connected to the home hub, is it a direct Ethernet cable, or wireless? Wireless is subject to interference and disconnects.
Does the problem still occur if you totally disconnect the TV BT (YouView?) box from the powerline adapter?
How many powerline adapters are you using, and is the xbox connected via its own slave adapter, or through a network switch?
I am thinking about possible interaction between the TV (YouView) and the Xbox.
Also. sometimes people connect powerline adapters incorrectly, so I made up this diagram.
There should be no interaction, but you could try with the TV disconnected.
If you are using BT YouView, then that does take priority over bandwidth, but unless you have a slow Internet connection, there should be plenty to spare.
What EA are saying, is that certain incoming coneections (ports) should be open, to allow communication with other users.
In theory, these connections should be automatically established by the home hub, using UPnP.
The home hub is not very good in that respect, so you will have to manually assign the ports needed.
I do not know which ports they would be, but there are quite a few forum members who do online gaming, so they may be able to help with this.
BT Guide for the Home Hub Port Forwarding with Home Hub