[noggin]

Out of interest - does your TV have an internal media player?  What happens if you play your Rec 709 UHD files in that rather than on the Shield TV? 

 Yes, my TV has an internal media player and it plays Rec 709 UHD files much better that Shield TV but it can't handle high bitrate like Shield TV.

I appreciate your generosity and your great experience and I'd like to ask a question risking being out-of-body. For me the best option is to shoot at 50p 10bit but I can't do it with my GH5. I can shoot only 25p 10 bit. Yes, I can make some tests and to edit those clips but it isn't the same than to shoot in Africa where there is red earth, a lot of light, I'm always in a hurry, etc. etc. In your opinion is it better to shoot 25p 10bit or 50p 8bit? I remember you I don't sell my documentaries and only I am the user (consumer), although I would like to get the best image quality with my GH5.  

What bitrate are you exporting at that your TV can't cope?

I'd try HEVC 2160p50 at bitrates from 20 - 40Mbs.

Personally I like the 50p look as it has a more realistic feel.  However most documentaries and dramas are shot at 25p for a more 'filmic' look.  You may be able to reduce bitrate a bit with 25p.