I repackaged a bunch of my mp4’s (mine are h265) as mkvs and the problem went away. There is another thread where support said the way some mp4s are muxed puts the audio packets out of order with the video and the seeking action is screwing playback. They are looking for an optimization fix, but no eta.
What i don’t understand is why plex is the only thing having a problem with these out of order mp4s.
I’m in the process of repackaging my entire library from mp4 to mkv, but it’s going to take me days.
Link: nVidia Shield "Your connection to the server is not fast enough to stream this video"