AltaVault securely stores information such as the encryption key and cloud credentials in the secure vault. This secured file system is unlocked during the boot process, and uses a key that is tied to elements of the virtualization environment AltaVault was placed in at the time of first boot. If any of those things have changed (such as the host if you did a VM migration), this could cause the secure vault to not unlock. You should engage support to get this unlocked, and confirm the circumstances which triggered this in the first place. Once you get it unlocked, you should be able to restore operations since the encryption key in the secure vault will be available again.