XB6 bridge mode: not forwarding any ports nor able to access admin page
I have a XB6 gateway. Port 1 of the gateway is connected to a nest router. Port 2 is unused. Prior to putting it in Bridge mode, I could access the admin panel at 10.0.0.1
My goal is to port forward all traffic to nest router and let it's built-in firewall take care of blocking or routing traffic. Specifically, I've configured the nest router to forward ports 8001 (tcp) and 51515 (udp) to the raspberry-pi behind it. I've verified this port forwarding works by directly accessing the ports on the router and seeing it route the traffic to r-pi as expected.
However, now I've turned on bridge mode on the gateway and noticed a few things I wasn't expecting, nor know how to fix:
1) I don't see the gateway forward any ports. If I access http://(my external ip):8001 it does not forward any traffic to the nest routers port 8001. Online port scanners show that port 8001 is closed/inaccessible.
2) The internal IP of the gateway seems to have changed to 172.16.12.1 based on the wan IP shown in nest home app as well as tracert requests routing through it before hitting the internet.
3) I can no longer access the admin page at either http://10.0.0.1 or http://172.16.12.1
Based on online instructions, it seems I should be able to access the admin interface after bridge mode is enabled (for example, online instructions mention accessing the admin ui to disable bridge mode in future if one changes their mind).
Any suggestions what I could be doing wrong? I'm a home internet user fwiw. My nest router has a WAN IP of 172.16.12.128, internal/LAN IP of 192.168.86.1.