I have several networks comprised of an MX100 hub and MX64 spokes.
I also have two non-Meraki peers, both Sonicwall devices.
I have a few users that use client VPN on Windows 10 machines.
Until about a day ago, all were working normally. A day or so ago, the site to site VPNs went down but the non-Meraki peers remain connected. The client VPNs can no longer connect, with Event Viewer indicating error 809.
These clients VPNs are on various networks, personal, corporate, etc. No firewalls are in the way and there are no NATs between them.
I tried adding the registry entry indicating in some troubleshooting guides for error 809, with no change.
Even on the still connected non-Meraki peers, no traffic will pass through. Even ping doesn't work from one firewall to the other.
Note that no configuration changes have been made. All was working one day, and not the next.
The firewalls all indicate that are connected as normal and behind VPN friendly NATs.