Admittedly, I am not proficient with Jails, but I need to know: Where did that IP address come from? Is that your public IP? That is not inside private address space. Shouldn't there be an address specified there that is inside the same private subnet as the TrueNAS? How would the jail be accessible to anyone if that is the IP, unless there is a router with a static route or a port forward? Even then, that IP address should not be your public IP. A port forward rule (not even needed with Plex) could forward to a private IP inside your network, but you would still need a private IP for the Jail, unless you bridge the NAS interface, in which case you could use THAT private IP address in the port forward rule.
Maybe my inexperience with Jails is showing here... but I know how VM routing is done in other hypervisors, and that seems off to me.