And yet
1-Some people report the same sort of problem with Roku.
2-Some people experienced the problem with ATV, and the problem subsequently went away or
3-got fixed.
I myself did something that appeard to fix poor NF quality after the AT software update that started this thread. At my request, NF "deauthorized" my ATV box. When I reauthorized it (signed in), the NF performance improved dramatically. I can't provide quantitive information, but it looks good and there is no pixelation.
It seems to me (I have read far more than ten posts on this) that a number of factors combine to make this issue hard to understand and pinpoint. One of the more telling pieces of information was, to my mind, that NF has servers that are not all alike. When I found this out, it suggested a possible explanation for why the de- and re-authorizing process cured the problem for me. My ATV box was now pointing to a server that was more friendly.
Obviously, your mileage may vary.