VPN issues for colleagues working at home

Hi all,

We have a RADIUS server setup that users connect to via Windows VPN connection, and now with many full-time staff working from home some issues have come up where several colleagues have been unsuccessful connecting.

I've exhausted a number of things including:

• turning firewall off temporarily
• changing their home network connection from public to private
• Windows and system updates
• removing and re-adding all the WAN Miniport network adapters
• changing VPN server address from friendly name to IP
• changing the VPN's protocol to PPTP (what other successful connections are using) from automatic, though automatic has worked fine before and is working fine for the majority of staff
• verifying that no one was using a static IP address (had issues with that one time in the past)

...the list goes on.

Common denominator between the handful of colleagues who can't connect is they all have fairly recent service through Spectrum and are using Spectrum issued routers (Sagemcom I believe [never heard of before]). I even tried adding a custom firewall rule on the router to allow PPTP for outgoing and later outgoing/incoming, as the list of custom rules did not include one for PPTP nor did it allow the VPN connection to be successful when the firewall was set to "Low - Allow All". It's possible I created the rule wrong as I wasn't entirely sure what to put for the port (i tried 1723 as well as leaving it blank), but nonetheless I was still striking out.

I still have a gut feeling that it's the Spectrum router hardware, but after hours reaching out to them and getting escalated to tier 3 support they insist it has nothing to do with anything on their end. One thing that could possibly clear their culpability is that a hotspot and phone tethering of the workstations in question wouldn't work either, but neither did my own computer when using my iPhone as a hotspot (maybe iPhone doesn't do PPTP either?). My computer connects to the VPN fine when connected to my home WiFi network (Spectrum but with own hardware).

I come to you, the wise and talented individuals of r/networking, in hopes that someone might have a suggestion or perhaps even a similar experience with definitive solution. Many thanks in advance, as I know I've pooled very helpful responses to questions I've had in the past.

With gratitude...