your pms server dashboard has real time bandwidth monitoring, if you see the graph having solid peaks ~100-110mbs while the client is buffering then it certainly sounds like the connection to your tv (regardless of wired/wireless) is simply not fast enough for that show’s bitrate.
4k is difficult, and smart tvs apps are often not quite as smart or good as people expect or want.
see also @ Plex, 4k, transcoding, and you - aka the rules of 4k - a FAQ for a lot of info and discussion.
