mac: migrated VPN server broken with MacOS Catalina

My Mac mini has been working fine with macOS Mojave as a VPN server following the migration method described at https://developer.apple.com/support/downloads/macOS-Server-Service-Migration-Guide.pdf, but after The update for macOS Catalina there are problems:

VPN clients connect well in the internal network, but not in an external network; Which makes the VPN server a bit useless! I can confirm that everything worked fine with the server running macOS Mojave, and my iOS 13 and iPadOS 13 clients have connected very well; It is the update to macOS Catalina on the server that has caused this problem.

Here are the registry entries for a failed connection:

2019-10-12 20:42:38 CDT Incoming call … Address given to customer = 10.0.0.224
Saturday, October 12 20:42:38 2019: Directory Services Authentication Complement Completed
Saturday, October 12 20:42:38 2019: Directory Services Authorization Complement Completed
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:38 2019: Incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:38 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:38 2019: L2TP sent SCCRP
2019-10-12 20:42:38 CDT Incoming call … Address given to customer = 10.0.0.225
Saturday, October 12 20:42:38 2019: Directory Services Authentication Complement Completed
Saturday, October 12 20:42:38 2019: Directory Services Authorization Complement Completed
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:38 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:38 2019: Incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:38 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:38 2019: L2TP sent SCCRP
2019-10-12 20:42:40 CDT Incoming call … Address given to customer = 10.0.0.226
Saturday, October 12, 20:42:40 2019: Directory Services Authentication Plug-in was initialized
Saturday, October 12 20:42:40 2019: Directory Services Authorization Complement Initialized
Saturday October 12 20:42:40 2019: Post_entry SCDSet () failed: Success!
Saturday October 12 20:42:40 2019: Post_entry SCDSet () failed: Success!
Saturday October 12 20:42:40 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:40 2019: incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:40 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:40 2019: L2TP sent SCCRP
2019-10-12 20:42:44 CDT Incoming call … Address given to customer = 10.0.0.227
Saturday, October 12 20:42:44 2019: Directory Services Authentication Complement Completed
Saturday, October 12 20:42:44 2019: Directory Services Authorization Complement Initialized
Sat October 12 20:42:44 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:44 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:44 2019: Post_entry SCDSet () failed: Success!
Saturday, October 12 20:42:44 2019: incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:44 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:44 2019: L2TP sent SCCRP
2019-10-12 20:42:48 CDT Incoming call … Address given to customer = 10.0.0.228
Saturday, October 12 20:42:48 2019: Directory Services Authentication Complement Completed
Saturday, October 12 8:42:48 PM 2019: Directory Services Authorization Add-in was initialized
Sat October 12 20:42:48 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:48 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:48 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:48 2019: Incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:48 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:48 2019: L2TP sent SCCRP
2019-10-12 20:42:52 CDT Incoming call … Address given to customer = 10.0.0.229
Saturday, October 12 20:42:52 2019: Directory Services Authentication Complement Completed
Saturday, October 12 8:42:52 PM 2019: Directory Services Authorization Completion Completed
Sat October 12 20:42:52 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:52 2019: Post_entry SCDSet () failed: Success!
Sat October 12 20:42:52 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:52 2019: Incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:52 2019: L2TP received SCCRQ
Sat 12 Oct 20:42:52 2019: L2TP sent SCCRP
2019-10-12 20:42:56 CDT Incoming call … Address given to customer = 10.0.0.230
Saturday, October 12 20:42:56 2019: Directory Services Authentication Complement Completed
Saturday, October 12 8:42:56 PM 2019: Authorization supplement for initialized directory services
Saturday October 12 20:42:56 2019: Post_entry SCDSet () failed: Success!
Saturday October 12 20:42:56 2019: Post_entry SCDSet () failed: Success!
Saturday October 12 20:42:56 2019: Post_entry SCDSet () failed: Success!
Sat 12 Oct 20:42:56 2019: Incoming call L2TP in progress from & # 39; xx.xx.xxx.xxx & # 39; …
Sat 12 Oct 20:42:56 2019: L2TP received SCCRQ
Sat 12 Oct 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