VPN issue since January 2024 Firmware update

I had the old round tower router that worked fine for working from home up until their firmware upgrade in January (2024). This is the month conectivity changed.

It was a wide-spread report across Reddit and other tech sites by customers that all of a sudden post firmware updating they lost work VPN access.

I had not swapped out the router because I have access to the work tools I need otherwise. This past Saturday I decided to call TM, explain the issue and they flagged down a store that had the newer router. I went there and swapped it out, receiving the TMO-G4AR model. Connected the new router and same issue.

My issue:

Windows 11 Pro on PC less than a year old.

I have a LAN cable connected from the TM router (tried both LAN1 and LAN2) to my PC. 

Connect to my work VPN works fine - will explain further

Post VPN connection I start Remote Desktop and then RDP to my work PC, entering my domain login info

Remote Desktop opens my work PC and I have navigation, etc

Up to several seconds after, VPN disconnects, almost like crashes out, and then I lose RDP as well

In Event Viewer > Application, I filter by RasClient and see connection to the remote access server was established, successfully connected, then the next entry about a minute later is the vpn has terminated - error on the termination is 829, which is essentially an ERROR_LINK_FAILURE

I reconnect again, get remote desktop, poof, same termination, same error

I have spent countless hours with two IT guys at work on this, performing a multitude of tasks and settings changes, same outcome occurs

I had hopes that swapping the old router out for the new one would resolve the above issue but it has not

To mention, I also have AT&T internet. Not their home internet similar to T-Mobile, but their regular high speed internet - in from their street box, to our complex, to my unit, to their router, and then LAN cable to my PC. I unplug TMobile, plug in LAN cable from AT&T and it works fine.

Again, prior to the January firmware update in the elder router, this worked flawlessly. Im not sure what the firmware changes are on this new router I picked up three days ago (?) but maybe it has a similar issue. Maybe.