The CPU in your NAS doesn’t have support for Intel QuickSync
So it cannot use Plex’s ‘Hardware Transcoding’.
And you have additionally activated a subtitle which needs to be “burned” into the video stream (because the TV cannot decode it on its own).
This can only run on one of the cpu cores, instead of all in parallel. So it is totally expected that the CPU is transcoding and is maxed out with it.
Thank you Ottokerner
but No even without SRT subtitles enabled NVidia sheild PMS on transcode H264 to H264 (video only)
While the same movie run on native plex app of LG even with SRT subtitles does not need to transcode
Im comparing Two Clients PLEX client for NVdia sheild Makes my cpu 97% while PLEX client for LG works direct play SAME movie Equilizer 2 same server Intel® Xeon® Processor D-1521 (6M Cache, 2.40 GHz)
Then show me the server logs when you played this movie on your Shield and I can tell you exactly why it transcodes.
Most likely it has to do with some bandwidth limit that is set somewhere.
Plex Media Server Logs_2018-12-23_22-22-28.zip (2.9 MB)
today log with no problem transcoding
Hi again
strangely I rein installed PLEX app on the Sheild (had to do it for google play account) and installed the update as well and voila the same movies are not transcoding 
i attached all the server logs today when the problem is solved and yesterday when the problem was there are these the logs you needed or only the media server log ? thanks maybe this would help some other users about what happened I have the latest update for Nvidia sheild installed
YEST log problem transcoding h264 to h264
Plex Media Server Logs_2018-12-22_14-20-25.zip (2.2 MB)
There was one playback event, where the transcoding was caused by a subtitle which was allegedly not compatible with the Shield.
Maybe the latest Shield software update rectified this, so the Shield can now play this subtitle directly.
(I am no expert for the Shield, so I can only guess here.)
