An invocation ID is an identification number that uniquely identifies a database within Active Directory. Invocation IDs change during the restore process to make sure replication is consistent.
When domain controllers are restored and the Invocation ID resets, other domain controllers will forward changes to the restored domain controller. If domain controllers do not undergo proper restoration, Invocation IDs may not be able to perform a proper reset to match other controllers and may cause replication problems throughout an organization.
Invocation IDs are also important to fix update sequence number (USN) rollbacks because a successful fix involves resetting Invocation IDs for the AD database. If these numbers aren't reset, there will be gaps between the restored domain controller and other domain controllers throughout Active Directory.