Hi @rups0911,
It’s very strange that you get worse by disabling IPV6 support… In fact the problem is complex and seems to be linked to several things… a real headache 
By the way, on my side, I’ve deactivated “auto connection” from the Plex LG client because we are many at home to use Plex and I set a PIN code in order to “keep” my kids from watching anything on PMS.
Option I have deactivated from Plex LG client :
The Plex login screen on LG TV :
This settings can also be significative because it forces the Plex Client to connect to PMS directly after launching and, may be, it “pre-initializes” the connection before the “network not available” error happens.
It’s just a guess… if you have time, you could try that.
Regards
