It looks like you omitted the disk type, as you can see in the
CLI reference:
Parameter
type=[logon|boot] defines a
disk type, which can be either logon-time disk or boot-time disk. The former is mounted upon user logon, the latter is mounted upon system boot. The default value is logon.
In your command line you created a disk that is only mounted at logon. It means it will be mounted much later when a user logs on, or not at all if a user doesn't log on, while the Server service starts early in system boot.
Simply add "type=boot" in your command and things should work as expected.