On an upgrade of VirtualBox Whonix from 13 to 14, it’s necessary to set the include statement in /etc/apparmor.d/system_tor, as I’ve posted elsewhere. Otherwise the Connection Wizard will fail.
I noted that on an upgrade, the system starts following the Tor settings as applied in the previous 13 version, and whonixcheck succeeds. However the Connection Wizard also starts, and this is somewhat confusing. If one cancels that wizard then the gw is functional.
It may be as well to include some helpful comment in the upgrade instructions about this.
Otherwise, as I said above, imo the process is smooth and 14 works well as upgraded system.