In a scenario where an organization has multiple active directory domain controllers (DCs) that replicate with one another, the Service Manager Active Directory Connector may not function correctly when DC switchover occurs. In this scenario, the connector can potentially miss some updates that are made on the domain controller.

Additionally, the connector may have the same problem for a single domain controller that has been restored from backup

For all the details and a link to download the hotfix please see the following article:

KB2561415 - Active Directory Connector does not synchronize new updates after you switch domain controllers