I invested far too much time for this. I was wondering why suddenly my VPN connection was not working anymore. I set up a complete new environment and tighten the security and created some Administrators for the servers and denied the built-in Administrator for all servers except the Domain Controller.
To keep it short:
My VPN does not work when I have a special character in my password. I have the é in my password > does not work. I replaced it with ? and it worked. But the login worked fine in the old portal (after I updated the search query under authentication). So the problem is the character. A bug?
Just for information if someone is interested. I was willing to change the encryption of the VPN (using L2TP with Windows 10) because it was only working with 3DES and stopped working after I replaced the IPSec policy. I was able to modify my VPN connection with PowerShell:
Set-VpnConnectionIPsecConfiguration -ConnectionName "xx VPN" -AuthenticationTransformConstants SHA256128 -CipherTransformConstants AES256 -EncryptionMethod AES256 -IntegrityCheckMethod SHA256 -PfsGroup ECP384 -DHGroup ECP384
Unfortunately only PAP works :(
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