I've been using Plex with my Samsung TV for years now. Recently I've been having a problem when launching the Plex app on my Samsung TV. Upon opening, my local server is shown as unavailable. I then navigate to the server list in preferences where my server is shown as "undefined : undefined server_name". From there I can temporarily resolve the issue by deleting my server and adding it again using my PMS' local IP (192.168.0.3). This works until the app is closed either via closing the app or powering off the TV.
I don't remember exactly when this started but it might be since PIA's latest client update. I really am not sure though.
/// MY SETUP ///
Windows 10 64bit (server)
VPN (Private Internet Access) (server)
Samsung TV (main streaming device and only problem device)
Samsung Galaxy S6 Edge (as secondary testing device)
TESTS (all while connected to local network):
OK - Samsung TV to PMS without VPN
FAIL - Samsung TV to PMS with VPN
OK - Samsung Galaxy S6 Edge to PMS without VPN
OK - Samsung Galaxy S6 Edge to PMS with VPN