Thanks for the stream capture. Investigating diagnostics provided by @damonc_nz here shows the issue being streams take a while before they start and the transcoder is timing out the device after 5 seconds.
It was the additional diagnostics from RawCap…exe to capture 127.0.0.1 packets in pacp file that helped establish that. With a pcap capture of Plex failing and Plex logs and then a rawcap.exe pcap capture of the curl.exe run
If you are happy looking into RawCap.exe - link in this post Unable to play or record Live TV then that would give more examples of the number of seconds the tuners are taking to start streaming
