Nvidia Shield 4K 2019 - TUBE - 4K Stuttering Issues

Plex Players Streaming Devices
3

Nvidia Tube Shield TV 2019 Non-Pro Stutters & Crashes on 4K UHD MKVs (nVidia officially blames Plex app) - Plex Players / Streaming Devices - Plex Forum

This here is what you are up against. Good luck. I would probably just try to return the tubes or sell them and buy pros as this issue will likely never be resolved any other way.