Hi romburner,
have your found a solution?
I have a 65" LG TV, which has a similar issue (I’m using a Synology DS218play as my NAS running the Plex server and the LG webOS client app, both uptodate). Whenever I try to use any kind of subtitles, I get constant buffering (after approx 10 seconds of video playback). This is extremely annoying to the point where I wish I had chosen Samsung again as my new TV. I never had this issue with Tizen 
