I am finding Plex player on Nvidia Shield to be a bomb. I now mostly use Kodi… here is why…
Videos are not played full screen anymore, they used to. Everything I have tried to change that has not worked.
Video and audio constantly get out of sync like the old Godzilla movies. Sometimes by stopping the playback, getting out of it and then resuming, it corrects itself, but not always.
Video has started stuttering
The interface has changed so that trying to just stop a video in play by using return/back brings you not to where you thought you were going.
As a compare, I also have a Roku Ultra box and none of this happens on it. Only on the Nvidia.
Are you using the beta versions? I only run the release versions due to all the beta issues. Other than a few UI bugs I have no issues with any of my movies playing.