Fibre NH20A port forwarding issues: works for some ports, not for others

So here's where I'm at. My Technicolor NAH (FXA5000) is working. 
How? Not entirely sure, but I believe it was an IPv4 firewall issue and not port forwarding that was the culprit. The issue that I was having (and I'll reiterate that this was MY experience) was that the port forward rules were valid and the specific ports themselves WERE open. What I determined was that the IPv4 firewall rule set would never completely set itself to NAT-ONLY. I tried bypassing the NAH, using my T3200M, bridging every single port. Heck, I even borrowed a UDM pro and dropped the GPON SFP into it. All of these worked as expected. The only thing that didn't was running traffic through the NAH in gateway mode where the ports I had forwarded would test as open, however, the traffic wouldn't be visible on the internal network (thank you wireshark). This brought me to concluding there was a firewall/traffic filtering issue at work.

My solution? I was able (through friends and people I used to work with) to get in contact with the team that does consumer device testing and pled my case, complete with documentation, Visio diagrams and my hypothesis. I never received a definitive answer, but I left the NAH live for a couple of days, performed a factory reset on the device, and everything worked as expected. I've never received any follow-up comms explaining what changed, if anything, but it does seem to work now.