I get exactly the same issue direct play is fine. Soon as it needs to transcode EAC3 it just doesn’t load.
Direct play for me is fine on Roku Express 4K HD. I am using Plex docker in Unraid. I have just started converting file using ffmpeg:-
this just does the audio and doesnt recode the video so is fast.
ffmpeg -i “filename.mkv” -vcodec copy -acodec aac -strict -2 output.mkv