Intermittent issues observed in the AD synchronization project: certain attributes are not consistently synchronized across all sync cycles

We have OIM 9.2.1

We have a synchronization project with Active Directory in which we need to synchronize  attributes  like  ExtensionAttribute15 and Mail

In many cases, these attributes are successfully synchronized to AD, but in many others, they are not. Most of the update run after midnights following automatic porcesses.

And if we then upgrade a non updated attribute (in AD) from OIM mannually it works..

Extract from the JobHistory table for a user:

 <Op Columnname="ExtensionAttribute15" Type="Value" ValType="String" AlreadyApplied="True"><OldValue /><Value>XXXXX</Value></Op>


So it should send teh new value to AD, but it did not 

Same for Mail attribute

We don’t understand why OIM sometimes synchronizes theses attribute and other times it does not.

In Synchronisation Editor, we don't have any errors.

Any idea what  can be the problem or how we can debug this ? 

Thank you for your help.