I have a similar issue. Content such as Jumanji & DowntonAbbey would not play, period. During my anguish I tried to adjust everything however the HDR, Chroma etc settings did alter the colour to a slight degree. [Sony XBR55x800E + AppleTV 4K ...]
The solution to some of the issues was to force download a 1080m4v or mp4 file rather than the HLS video package. Not 100% but almost a good answer.
Once I had the 1080 video [iTunes Store] mp4/m4v... some titles would appear but still not play until I rebooted everything, change settings and restart everything again. everything - router, hubs, switches, Mac, AppleTV, everything again and again. 4K purchased content still does not play via home sharing on the appleTV, or at least I can't get it to play unless I stream it.
I had success by "Remove Download" (in TV App) and set prefs to "best available", uncheck multichannel & HDR. Download again and perhaps restart.
I should mention everything else was playing and performing perfect except for perhaps 3 very recent movies only.
A Hmmmm moment.