Disable and re-enable your Host Only Adapter and reset your DHCP server(if you are using it in the Host Manger part of Vbox). Then try to log in again into your VM. Hopefully this will help you fix this.
Why did this happen?
There are rumors that from a recent Windows 10 update that Windows is not setting a proper default settings for VBox ( no idea which setting it is. Apparently, this has been a thing since v5 of VBox). By disabling/re-enabling the Host Only Adapter, it fixes that default setting (whatever it is :).