I have commented on this discussion topic back on November 2017 when this stopped working while we were on a trip and had downloaded movies to watch on our TV in the Mobil home. Downloaded movies worked up until that point.
Since then I have tested it with my iphone which has an older iOS 10.3.2 and it still works. I download a movie on my phone with netflix and it plays with my lightning AV adapter via hdmi. I don't know what version my netflix is but I am not updating till this gets resolved or maybe never.
Since then there has been another iOS update to my ipad to 11.2.2 and yesterday (1/15/2018) there was a netflix update too but this still did not fix the problem. Downloaded movies do not play on the TV using the lightning AV adapter. I get sound but no video in the TV.
I also have Amazon prime and downloaded movies play fine. Which leads me to believe its a netflix problem but Apple should vet its apps on the app store so its also their fault. The reason this is not a big issue is mainly because we are a small few that use it this way. Most folks stream and only download to view on planes or while traveling on their ipads or iphones, few actually connect a lightning adapter via hdmi to a TV. Yet here we are!
The real ****** is that Netflix nor Apple have anything posted regarding this and have all of us wondering what happened? Yes Netflix could change its policy and say something like downloaded movies are only for mobile devises etc although that would be a bad business move because Amazon allows it and movies over itunes also work. In any case they could change their policy but that needs to be posted somewhere or some information found somewhere. There should be a better way to voice ones frustration or complaint about this. I too am seriously thinking of canceling netflix mainly because i have cable and amazon and this it not getting any attention.