Task finally fails with error message:
Some of objects are still not replicated to all active domain controllers. AD replication may take up to several minutes. You have to troubleshoot AD replication only if this task has finally failed (all attempts have failed).
This task queries all registered in OA Domain Controllers in order to verify that an object (see task description for an object name) has been replicated and exists an all controllers. Failures of such tasks can be caused by Active Directory replication issues.
In case when task resubmission does not help, one should investigate Active Directory replication issues. It can be helpful to get an object name from the task description in order to have an instance which can not be replicated. For details on troubleshooting Active Directory replication, please check the following article on Microsoft TechNet: Troubleshooting Active Directory Replication Problems.