ARRIS G36 Firewall VPN Disconnecting Issue

I'm requesting escalation of an issue involving my (owned) ARRIS G36 modem/router and its Xfinity-provisioned firmware. My G36 has the latest firmware (AR01.05.020.13_032624_735.NCS.20). 

I connect to a corporate VPN for work (FortiClient 7.4.7.2003 VPN, latest version). The VPN disconnects after 20-30 minutes. I have isolated the issue to the G36's IPv4 firewall. I have conducted the following testing:
- IPv4 Firewall Medium security setting: disconnects after 20-30 minutes
- IPv4 Firewall Low security setting: disconnects after 20-30 minutes
- IPv4 Firewall Disabled: stable for my work day
- Cellular hotspot used to connect to internet then VPN: stable for my work day
- Issue occurs on both G36 Ethernet and Wi-Fi

- Issue occurs on a different laptop and under different versions of Forticlient
- General Internet connectivity remains active after VPN disconnects
- FortiClient frequently reports "dead peer detection" related error messages on disconnect

Please escalate this as a potential ARRIS G36 firmware/firewall compatibility issue and confirm whether AR01.05.020.13_032624_735.NCS.20 is the latest Xfinity-approved firmware for the G36.

Thank you!