Adding my comment on this as we are experiencing the same issue since the windows 10 2004 update.
The L2TP vpn client now constantly fails to connect to meraki client vpn.
The settings of the windows 10 gui and the control panel adapter page appear to be in conflict. By which I mean that when you set the VPN to password authentication in the Windows 10 Settings gui it resets the network adapter security tab settings and then when you edit the control panel network adapter properties for the vpn connection under the security tab to allow the protocol for PAP it resets the windows 10 VPN gui to general authentication.
The two therefore remain in constant conflict and setting one, unsets the other...