I have a couple of customers whose L2TP-IPSEC VPN Windows 10 client connections stopped connecting to the company VPN.
To fix this:
- Uninstall all the WAN Miniport devices, under Network Adapters, in Windows Device Manager.
- Then Scan for Hardware Changes and let Windows reinstall the WAN Miniport devices.
- Then try your L2TP WPN Client. It's bound to work!