Migrated VPN server broken with macOS Catalina

My Mac mini has been working just fine with macOS Mojave as a VPN server following the migration method described in the [macOS Server Service Migration Guide](https://developer.apple.com/support/downloads/macOS-Server-Service-Migration-Guide.pdf) , but after upgrading to macOS Catalina there is trouble. The VPN clients connect just fine on the internal network, but not on an external network; which makes the VPN server a bit pointless! I can confirm that all was working well with the server running macOS Mojave, and my iOS 13 and iPadOS 13 clients have been connecting just fine; it is the upgrade to macOS Catalina on the server that has caused this problem. Here are the log entries for a failed connection: 2019-10-12 20:42:38 CDT Incoming call... Address given to client = 10.0.0.224 Sat Oct 12 20:42:38 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:38 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:38 2019 : L2TP received SCCRQ Sat Oct 12 20:42:38 2019 : L2TP sent SCCRP 2019-10-12 20:42:38 CDT Incoming call... Address given to client = 10.0.0.225 Sat Oct 12 20:42:38 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:38 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:38 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:38 2019 : L2TP received SCCRQ Sat Oct 12 20:42:38 2019 : L2TP sent SCCRP 2019-10-12 20:42:40 CDT Incoming call... Address given to client = 10.0.0.226 Sat Oct 12 20:42:40 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:40 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:40 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:40 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:40 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:40 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:40 2019 : L2TP received SCCRQ Sat Oct 12 20:42:40 2019 : L2TP sent SCCRP 2019-10-12 20:42:44 CDT Incoming call... Address given to client = 10.0.0.227 Sat Oct 12 20:42:44 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:44 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:44 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:44 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:44 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:44 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:44 2019 : L2TP received SCCRQ Sat Oct 12 20:42:44 2019 : L2TP sent SCCRP 2019-10-12 20:42:48 CDT Incoming call... Address given to client = 10.0.0.228 Sat Oct 12 20:42:48 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:48 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:48 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:48 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:48 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:48 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:48 2019 : L2TP received SCCRQ Sat Oct 12 20:42:48 2019 : L2TP sent SCCRP 2019-10-12 20:42:52 CDT Incoming call... Address given to client = 10.0.0.229 Sat Oct 12 20:42:52 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:52 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:52 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:52 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:52 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:52 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:52 2019 : L2TP received SCCRQ Sat Oct 12 20:42:52 2019 : L2TP sent SCCRP 2019-10-12 20:42:56 CDT Incoming call... Address given to client = 10.0.0.230 Sat Oct 12 20:42:56 2019 : Directory Services Authentication plugin initialized Sat Oct 12 20:42:56 2019 : Directory Services Authorization plugin initialized Sat Oct 12 20:42:56 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:56 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:56 2019 : publish_entry SCDSet() failed: Success! Sat Oct 12 20:42:56 2019 : L2TP incoming call in progress from 'xx.xx.xxx.xxx'... Sat Oct 12 20:42:56 2019 : L2TP received SCCRQ Sat Oct 12 20:42:56 2019 : L2TP sent SCCRP 2019-10-12 20:42:58 CDT --> Client with address = 10.0.0.224 has hung-up 2019-10-12 20:42:58 CDT --> Client with address = 10.0.0.225 has hung-up 2019-10-12 20:43:00 CDT --> Client with address = 10.0.0.226 has hung-up 2019-10-12 20:43:04 CDT --> Client with address = 10.0.0.227 has hung-up 2019-10-12 20:43:08 CDT --> Client with address = 10.0.0.228 has hung-up 2019-10-12 20:43:12 CDT --> Client with address = 10.0.0.229 has hung-up 2019-10-12 20:43:16 CDT --> Client with address = 10.0.0.230 has hung-up I’m currently using the built-in VPN on macOS Catalina 10.15.1