Nighthawk AX2400 (RAX30) not forwarding port 8123

My old N600 (which has been great for the last 12 years) decided that yesterday was it's last day in my service (she died) so I brought a Nighthawk AX2400.

I have a Home Assistant server running and need to set up port forwarding to it.

It uses port 8123 natively but setting up the router to take port 8123 as the external port does not work. If I choose a different port, say port 9000 as the external port it works just fine.

This does not work:

This does work:

Does anyone know what's happening? The logs look as though the connection is made, but the browser trying to make the connection eventually just times out.

I have set up port forwarding many times on different routers in the past and never encountered this, perhaps it's a bug in the firmware when both external and internal ports are the same??

When I do an nmap scan with port 9000 open it gets reported as open, but configured for port 8123 it does not.

Secondary question:

nmap shows several ports open that I cannot find any setting that would cause them to be open, I know I can explicitly block them, but why are they open without my consent? Am I simply missing a setting somewhere that enables their service?

I understand why some are open automatically, but others I should have control over, or is this just how things are done these day? (I'm oldskool)

Ports in question:

22/tcp filtered ssh
23/tcp filtered telnet
139/tcp open netbios-ssn
445/tcp open microsoft-ds
8200/tcp open trivnet1

Thanks 😊

Firmware version: V1.0.6.74_1