I made this thread a back in mid august and was told that the bitrate is probably too high. At the time I was watching the first episode of https://www.pbs.org/kenburns/prohibition/ that would stutter to the point that the video would freeze and than start playing from the start sometime through the episode.
Than the next day I was watching Prison Break season 1 Episode 1 and it would play fine at the start but started stuttering and going out of synch with audio 20 min or so into the first episode.
I reported the issue but was told there is nothing I could do. So I didnt bother watching netflix on my 4k+ since. I dont know what the version of Widevine netflix was using in august when I had the issue but I provided a log in that thread so maybe you can find it in there.
I can try today again and see how things are now