Plex iOS app (4.6.1) does not play movies off Thecus 4880, doesn't matter what format. TV shows played just fine in any format. So Samsung Smart TV Plex application or web access through browser work just fine with any format.
When looked at the log, found this line:
"Jan 14, 2017 17:26:50.914 [0x7fc45e559710] ERROR - File requested for photo transcode is over maximum size of 104857600 bytes, refusing to transcode"
Note above that Plex Media Server refers to file as photo, whereas request comes for a movie.
Any ideas what to try?