S33 Possible Firewall?

Sequence Diagram of my network:

ISP → S33 (previously SBG6580) → Google Nest Wifi → wlan local network

                                                                                |→ eth0 Raspberry Pi w/ PiHole + PiVPN (port 51820)

Background:

I currently run a Raspberry Pi with PiVPN on my Spectrum internet. As of last week I purchased a new Surfboard S33 modem and it seemed to have blocked port 51820 OR has done something to conflict with the port management settings I’ve made within my Google Nest Wifi (Connected through 2.5 Gbs port).

I’m aware that modems do not have firewalls and the router is what provides this but the only constant for my port being closed has been this modem / the re-activation of my modem with Spectrum. I’ve even reached out 2-3 times to ask if they had anything in place that would block the port when it was re-activated.

My previous was a modem/router Surboard SBG6580 (Not 100% on the product code) that connected to my Nest Wifi via Ethernet but this one included a configurable firewall that seemed to allow port 51820 to be forwarded when I set it.

Questions I have:

• Spectrum offered to provision my internet? Could this help diagnosing the problem?
• Is someone familiar with possible securities setups for the S33? ( I see a security selected within the modem GUI)
• Is there any options other than factory resetting everything?

Configurations with Google Wifi:

• DHCP Reservations for the Raspberry Pi
• Custom DNS Server (Pointed at RaspberryPi)
• UPnP enabled (attempted disabling this)
• Port management for Pi with port 51820 enabled (found an article that said to attempt entering a single port (####) as a range (####-####) when filling this out as a hack. Didn’t work)

Things I’ve attempted:

• Restarted devices on system
• Removing + Re-adding the port management
• Removing the custom DNS server
• Resetting the S33 modem to factory and connecting it back
• Re-installed PiVPN
• Testing for the port status was done from laptop connected to mobile data hotspot and portchecker.co website.

Notable:

• Devices with Wiregaurd connecting to PiVPN are able to connect but can’t load a webpage.
• Internet is working as expected for Devices on my network

Thanks in advanced! I’ll do my best to return to edit this if I come across what is happening.