Yeah exactly as @nibbles states, a VPN will probably enable some routes on your machine routing table, as they are advertised by your provider so not much to do here except for disabling the network advertisement of your player/server, you are probably broadcasting traffic to all your neighbors. Just use PLEX online services to register your device and make it accessible.
I would bet than in your routing table an address space matches the 1.0.0.0 network or at least includes it.
Anyway I just feel curious on no adapter having other than non link-local addresses, your log shows that for IPv4 APIPA addresses are being assigned, and for IPv6 just local prefixes, so that is the reason I suppose PLEX is detecting VPN as primary interface and tries to broadcast outside your boundaries.
