I also have this issue.
I am using the following setup:
- LG CX
- Nvidia Shield 2019 Pro
- Plex App Version 9.19.0.177
- Plex Server Version 1.31.3.6868-28fc46b27
EDIT: I am running the plex server as a docker container on a different linux server. So not the built-in version of the Shield.
This issue can be easily recreated with the following Demo video from Dolby. Downloads Page - Demolandia
Just play the video with it’s truehd 7.1 audio channel and you can observe that the video timer does not start to count up from 0:00 until about 10 seconds of the video have been played. Then it starts to count up like it should, but the audio is already ahead.
Stopping and playing again does not help to solve the problem.
This file plays fine when using the internal Plex App of the WebOS system on the LG itself.
I do use audio passthrough so my tv can deliver the audio unchanged over eARC to my Sonos soundbar.
This seems to be very similar to the problem described here, which was either resolved, or no one replied in time before it was closed again (https://forums.plex.tv/t/is-anybody-working-at-plex-going-to-fix-the-nvidia-shield-startup-freezing-but-audio-plays-and-then-catches-up-fix/). @ChuckPa is there any way these cases are related? If i can help in any way, i would be glad to. Sorry to call you out of nowhere, but you were deeply connected to the problem the last time 
