My Home hub 5 recently failed, and was replaced. Since then, my BT YouView UHD box is losing connectivity. I get the "YouView has lost connectivity to the Internet" message and can also see the green link light on the back of the YouView box goes out. It is only for a second at a time and happens every few minutes, seemingly increasingly frequently until I power cycle the YouView box when it becomes less frequent at first, but over the course of the day becomes more frequent. I have switched Ethernet cables and ports on the hub with another device and the problem always remains with the YouView box. It is directly connected, no power line adapters/extenders/etc.
Seems too much of a coincidence that this has only happened since the router has been replaced, but can't think of a logical reason for the intermittent fault.
I have had the same but when turning youview on from standby on internet channels the UHD box says it is not connected to the router/internet. Rebooting the box does cure it but i have foud the quickest way to sort it it to pull out the ethernet cable from the box & put it back & it connects instantly.
I have had the box nearly 18 months & it has only started doing this recently & also a HH5 which is at sat next to the UHD box.