The Dolby vision, 4K on Netflix has moving grain, looks crap this was not always the case, when I switch to YouTube the 4K is stunning, do Netflix have enough capacity? Do virgin media mess with Netflix streams. I should be getting 350 mbs pay extra for this but lucky to get 200.
On some devices you can bring up stats in the top left that show the bitrate info, it is usually 15-16Mbps for 4K and I have no problem reaching that on Virgin Media. You can also run a speedtest within Netflix, I think it is under Settings or Help then select "Check network connection".