Windows Guest can VPN on Windows host, but not Linux Host

[xaric]

I dual-boot between Ubuntu and Windows 10 on a Lenovo T440s.

My guest VM is on an external SSD, Windows 10.

When I boot into Windows 10, my guest VM can VPN just fine. (MSChapv2).
When I boot into Ubuntu, the exact same guest VM cannot VPN, and I get an error:

Remote Access error 619 - A connection to the remote computer could not be established, so the port used for this connection was closed.

VirtualBox settings are identical on the Windows Host and Linux Host. There are no firewalls enabled, nothing special about the network connection (just your typical DHCP connection, no fancy settings).

I suspect that on a Linux Host, VirtualBox accesses the network card differently?

[socratis]

I suspect that on a Linux Host, VirtualBox accesses the network card differently?

No it doesn't. I suspect that the VPN client used is not working the same on a Windows and on an Ubuntu computer.

Just because an OS/program that runs in the context of VirtualBox has a problem, it doesn't make it a VirtualBox problem necessarily. You're having an issue that has most probably nothing to do with VirtualBox, so my suggestion would be to treat it as such, as a native problem with the OS or the application of the guest.

For example searching for "Remote Access error 619" returns plenty of results. None of them has anything to do with VirtualBox.