Did you use the plugin it self with standard settings (VNET DHCP and BPF on) or did you install plex in a manually created jail? (if so you also need to make sure those are enabled, most importantly VNET.
@klimisa is VNET enabled? If some is lan_ip actually the same subnet as you are now now vpns or such? If so please post OS/Jail versions and PMS version to (use pkg info or check freenas plugin UI for that)
The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: 10.0.0.0 - 10.255.255.255 (10/8 prefix) 172.16.0.0 - 172.31.255.255 (172.16/12 prefix) 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
Maybe you wanted to use 172.16.0.1/16 (12?) ? Do you really the need entire /16 for LAN, that’s a lot of hosts, so maybe there’s a mistake here?