I’ve said this many times, but never hurts to repeat;
smart tvs and most streaming devices are designed for STREAMING, from netflix and other streaming providers.
they are (generally) NOT designed to play high bitrate 4k bluray rips with HD audio via plex.
frankly it is a miracle that plex works as well as it does on the devices we have, and even moreso that we have a device like the shield that actually does work well enough with full 4k bluray rips.