I noticed that my VPN to a Meraki MX64 suddenly stopped working. It connected, but I got no traffic through the tunnel. I verified the settings several times, and completely re-configured everything, but the problem remained. This only seems to affect MacOS. On a virtual Windows 10 on the same Macbook, it worked fine. I colleague also had the same problem on his Mac.
The problem for me was the ordering of the interfaces in the routing table. MacOS does not use metrics in its routing table, instead there is a (static?) order of interfaces, that you can view like this:
~ networksetup -listnetworkserviceorder
An asterisk (*) denotes that a network service is disabled.