It seems that the latest version of the Plex App available for Android TVs (particularly the Shield TV 2017 -- which is the box I have) breaks 4K playback (and removes various useful options like being able to force direct play).
If you uninstall all updates and use the built in version available on the Shield TV then everything works fine again. I was trying to play 4K file and they would say things like:
"Transcode Reason: Bitrate or resolution exceeds the maximum allowed", even if you have the settings set to Maximum (for both local and remote).
Anyone else have this experience?