export operation to Active Directory Connector has failed

Azure AD connect health shows that our Directory Sync is unhealthy but everything seems to be working. The issue is “The export operation to Active Directory Connector has failed” and it shows “Please investigate the event log errors of export operation for further details.”

https://social.msdn.microsoft.com/Forums/Lync/en-US/af2ca4ff-1c97-47c3-a880-52a80c024e42/export-operation-to-active-directory-connector-has-failed?forum=WindowsAzureAD