I've recently noticed on the Non HD broadband channels that i randomly get these flickering black lines on the screen. Freeview channels are fine and the broadband HD channels are fine.
I have also recorded one of the problem channels and played it back to see if it happens at the same spot everytime, but it seems to only happen at random or when there are bright colours on the screen.
Things i've tried
Different HDMI cable
Factory reset my youview box
I'm not getting any internet problems/drop outs
Currently have the 4k UHD box and is wired up using ethernet cable supplied. I've only had the box/BT TV for one week now.
1080i (Interlaced) requires much less digital bandwidth than 1080p (progressive).
Interlacing generates the image over two successive frames, whereas progressive generates the image in one frame so the bit rate is much higher, and artifacts are likely show on the screen if errors occur.
You may be able to use 1080p if you have a very short high quality HDMI cable, and a TV which is capable of operating in that mode.
In practice you would find it quite difficult to see the difference between 1080i and 1080p.
1080p = 475MHz
1080i = 237MHz