Retention Policy not working - MSExchange Assistants Event ID 9028

Hi All,

I tried to put a retention policy on Deleted Items and Spam folders, but it doesn't work.

I tried get-mailbox | Start-ManagedFolderAssistant in EMS and it's the same result.

So I set log level to High with Set-EventLogLevel -Identity "MSExchange Assistants\Assistants" -Level High

And now I can see in eventlog event ID 9021 (MSExchange Assistants) for the request for each mailbox and after an error event ID 9028 (MSExchange Assistants) for each mailbox. (This, each time I run start-managedfolderassistant)

Ex:Service MSExchangeMailboxAssistants.Managed folder assistantinterrupted theprocessonetimeduring the processing ofthe mailbox(unknown)onthe databaseBALStandards (04af4f24-d8ae-470f-a7f8-ce15731acad5). The following exceptioncaused the error: System.NullReferenceException:Object referencenotset to an instanceof an object.
   à Microsoft.Exchange.MailboxAssistants.Assistants.ELC.MailboxDataForTags.Dispose(Boolean disposing)
   à Microsoft.Exchange.MailboxAssistants.Assistants.ELC.ELCAssistant.BuildMailboxData(MailboxSession mailboxSession, StatisticsLogEntry logEntry)
   à Microsoft.Exchange.MailboxAssistants.Assistants.ELC.ELCAssistant.InvokeCore(MailboxSession mailboxSession, StatisticsLogEntry logEntry, ElcParameters parameters)
   à Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(TryDelegate tryDelegate, FilterDelegate filterDelegate, CatchDelegate catchDelegate)
   à Microsoft.Exchange.MailboxAssistants.Assistants.ELC.ELCAssistant.InvokeInternalAssistant(MailboxSession mailboxSession, InvokeArgs invokeArgs, List`1 customDataToLog, Int32 totalAttempts)
   à Microsoft.Exchange.MailboxAssistants.Assistants.ELC.ELCAssistant.DoWork(AssistantTaskContext context)
   à Microsoft.Exchange.Assistants.TimeBasedDatabaseJob.ProcessMailboxUnderPoisonControl(AssistantTaskContext context, EmergencyKit kit)
   à Microsoft.Exchange.Assistants.TimeBasedDatabaseJob.<>c__DisplayClass9.<ProcessStoreMailbox>b__8()
   à Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(TryDelegate tryDelegate, FilterDelegate filterDelegate, CatchDelegate catchDelegate)

I set log level to MSADAccess to High. And now before events for MSExchange Assistants (9021-9028) I can see Warnings event ID 2128 (MSExchange ADAccess) for each mailbox : Process w3wp.exe (RemotePS) (PID=11016). Object CN=TOTO,OU=Utilisateurs,OU=Sites,DC=infra,DC=truc,DC=localnot found ondomain controllerAD2.infra.cg81.local.This mayindicate a problem withreplication orpermission.

It seems that Exchange Assistant can't find mailboxes (mailbox unknown, object not find,...) but replication between my domain controllers is verified and OK. Permissions seems OK but I'm not sure.