The ZyXEL EMG3425-Q10A has NAT Port Forwaring but it doesn’t seem to work well because the Remote Management section has been patched out. This causes the remote management screen to always boot on the IP that is the same as the Port Forwarding Default Server Setup. You need to do two things to fix this mess. First change the default server setup to be the target you normally will port forward to. Turn on a firewall on this host. Second, you need to forward the WWW and HTTPS rules to that host.
When adding additional rules, click “add” instead of apply. Add ports like 25565 to host minecraft or 27015 to TF2.
You cannot delete rules or you have to re-enter all of them in the right order. AGAIN.