Different stock quantity in R/3 and APO

What causes this issue?

The CIF comparison/reconciliation of transaction data (delta report)
has determined a stock
item with different quantities in SAP APO and SAP R/3.
The following are possible causes:
An <DS:GLOS.8554C86B3BAACE42817DEADBB261F52A>LUW</> was deleted from the
SAP R/3 outbound queue or from the SAP APO inbound queue.
A CIF <DS:GLOS.FD3EF445296FD74FB970B259AF19B0D7>postprocessing record</>
exists for the stock item.

System Response

How to fix this error?

Choose <LS>Iteration</>.
If the system continues to display the error after this,
choose <LS>Send to APO</>. The stock item is updated in SAP APO in
accordance with the current status in the SAP R/3 system.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.