If you often have to deal with replication problems in your Active Directory, you should switch on "Strict Replication Consistency". The following scenario could arise in the event of replication problems between 2 or more DCs:
An AD object is deleted on DC1, but the change cannot be replicated from DC1 to DC2 due to replication problems. In this case, if the replication problems last longer than the tombstone lifetime of the deleted object, DC2 reanimates the object previously deleted on DC1 after the replication problems have been resolved. The deleted object is therefore replicated back from DC2 to DC1. This can lead to serious problems, especially in poorly maintained overall structures. These problems can be avoided by activating "Strict Replication Consistency".
There are several ways to set the corresponding registry value:
Via the command repadmin:
repadmin.exe /regkey <DC> +strict
Where stands for the name of the domain controller. A wildcard * is also permitted if you want to quickly propagate this change to all DCs in the overall structure. The above command does nothing other than add the key specified below to the registry:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\NTDS\Parameters
Value Name: Strict Replication Consistency
Data type: REG_DWORD
Value: 1
