Content is 4K 100Mbs and is located on a ReadyNAS 516 which is also the PMS. Client is a Shield which should be able to handle the content w/o any transcoding. Playing the content will crash the Plex client after a few seconds of successful streaming.
I could be wrong, but I believe the issue causing the transcode is related to the extremely high bitrate.
I would run this through something like Handbrake and bring that rate down to see if you experience the same thing.
That would make sense, but does the Shield really need it to be transcoded in the first place?
In Plex client, set Display Information = on. Play the video and pull up the on screen controls (pause, etc). Look in upper left corner of screen. You should see a status with some info on why the video is transcoding.
Does the video have audio? If not, make sure you're running the current Plex client, v7.0.3. There was a bug in some of the early 6.x releases where video w/o an audio track would not play.
Can you successfully play other high bit rate movies? You might try the Jellyfish test files, http://jell.yfish.us/, and see they will play on your setup.