I’ve taken some 4k videos with my Mavic Pro and I’m having issues playing it back via Plex on the Roku or Samsung TV.
I attempted to playback the original as well as the edited video with no success. At best I got it to stutter 1 time.
Original Video = 4096x2160 23.98fps
Edited Video = 2048x1080 29.97fps
Videos are about 2 minutes long.
On the Roku I tried video playback at Original quality as well as transcoded to 20mpbs 1080p.
Most 4K video has a 3840 × 2160 resolution. A little research at my end, because the size seemed unusual, found the resolution you are using (4096 X2160) is classified as DCI 4K, a standard only used in the film and video production industry.
The unusual, extra width is probably confusing your TV, Roku and Plex and they just don’t know how to deal with it.
The original video has an aspect ration of approx 1.896:1. In order to fit on a 16X9 4K TV, the max width would be 3840. To maintain the original aspect, the height should be approx 2024.
I would try an edited version at 3840 X 2160 for 4K, or an edited version at 1920 X 1012 for 1080p.
I have no source video to try it myself, so just speculation that you need to keep the horizontal width equal or less than the resolution the TV and everything else is expecting. 
You are correct that resolution I was originally recording at was too much. I have changed the resolution for recording down to 3840x2160 and it now plays. It still takes a bit for it to load and play, even for just 1m videos.
This on a Plex VM that has 4 cores and 4GB of RAM.
