[asagala]

try (in KODI DS) "use full screen window" - ticked.

Also check your MADVR display modes match up, remove any 1080p modes in there, you wont need them if you are upscaling using MADVR which will be batter than your TV.

3D automatically drops to 1080p so you dont need that in there, I know only have 2160p23 in my display modes as I dont any other content.

 If use Kodi refresh rate matching and dont configure madvr switching profiles everything works as expected. Supports 1080p/24 and 4k hdr.

Only issue left is dropped frames when embedded subtitles are loaded. Seems to put a higher load on my CPU. 

 Reduced the gpu buffer from 8 to 4 and cpu buffer from 16 to 10 and now subtitles play great even on 4k hdr movies.