Can't get xfinity xb6 gateway to work in Bridge Mode with nighthawk router

Goal - To put my xb6 in bridge mode and use my Nighthawk AX4300 as the routher for my home

I currently run XB6 in router mode connected to Nighthawk in router mode, and I know this is not optimal / correct,

and you can't turn off DHCP for IPv4, only can uncheck IPv6

Router - RAX45 — Nighthawk AX6 6-Stream AX4300 - I chose the RAX40 from model dropdown as RAX45 was not listed.
Firmware Version 1.0.2.82. 

Comcast / xFinity GB service - testing at 950mb down at modem and 40mb up, getting what I'm paying for

Goal - To have my XB6 function as a dump modem in Bridge Mode connecte to Nighthawk which will be my main home router

Steps: 

1. Log into Xfinity XB6 Gateway (10.0.0.1 / 255.255.255.0) and Enabled Bridge Mode. Waited the minute while it rebooted

2. Connect ethernet cable direct from xfinity xb6 (tried both ports) to Nighthawk AX6 - RAX45, (internet port)

3. Powered down both my modem and router and restarted

Result: No Internet on Nighthawk,  Internet light is amber light. I tested using wired and wireless, no internet

One other piece of data, logging into Nighthwalk, it did grab an IP with 172.#.#.# and created DHCP based on that 
I normally use 192.168.1.1 before this reboot and a DHCP range like 192.168.1.10 - 192.168.1.150

What is the trick here? I have seen others in this forum also not have issues doing this simple task, once XB6 is in Bridge Mode, they have no internet

I tried plugging in ethernet to both ports of xb6, same result

What else can I do to troubleshoot this?

Thanks in advance!