So the secondary router (WNDR4500) is really the access point in my garage connected to the primary router (R8000). It’s an extension of the primary router. I thought the Ethernet ports would act like a generic switch but it doesn’t. The setup on the WNDR4500 has the port forwarding and many other settings like DHCP disabled. The 2nd post above documented from Netgear that port forwarding is disabled when it’s in AP mode.
I proved this tonight by plugging in a old 4 port 100Mb switch off the spare line and it port forwarded just fine.
Maybe other router brands will allow port forwarding through them while in AP mode but this one won’t.