Here the kicker it only does it on some 4k video files others seem to play fine even if they are bigger in size. Weird.
This has to do with the transcoder.
Unless its doing a direct stream to device, and your device is then transcoding the stream.
Either way the weakest link is either the unit hosting the file, or the unit playing the file.
Streaming 4K is not easy, especially if its .MKV 10bit HVEC file.
You would need something like a dedicated plex / kodi / emby host server with decent hardware if you want 100% playback without it freezing to buffer from time to time.
Example, my family members wanted foriegn subtitles which plex has, and it is a SMI.
SMI + 4K content means i need a dedicated transcoder hardware.
I was forced to get a Nivida Quadro P2000 just to do that. (FML) 400 dollar videocard just so they can watch my movies in foreign subtitles.
4K content is not easy to stream, unless your doing a direct stream from a NAS to PC.