Hybrid Azure AD Cloud Object’s UPN were not changed after the product update the domain name for the local AD object during Domain Move
Domain Move can not remove the domain because Hybrid Object’s UPN were not being updated in the tenant after Domain Move remove the domain from the local AD objects. Example below
Administrator wants to remove domain contoso.com from tenant contoso.onmicrosoft.com and replace their UPN with contoso.onmicrosoft.com domain name. However, there are still users with firstname.lastname@example.org stamped on the hybrid Azure AD Objects. Azure AD Connect was not syncing the on-prem object changes to the cloud, particularly for the UPN attribute.
Feature SynchronizeUpnForManagedUsers feature was not enabled. “Historically, updates to the UserPrincipalName attribute using the sync service from on-premises has been blocked, unless both of these conditions were true: