Routing Plex traffic through second WAN not working

[Offspring]

I've got a rule, where all traffic that's outbound on port 32400 (Plex) is supposed to go out through a secondary WAN/gateway, and it seemed to work yesterday but today the external Plex servers are no longer able to connect to my local server, but from everything I can see it should still be routing properly.

Is there a proper way of doing this type of routing?