No reference to purchase order found in mapping table for hash key &1

What causes this issue?

An existing purchase order should be updated based on new or changed
entries in buffer table RPO_D_ITEM_BUF.
However, the system cannot find an entry in mapping table RPO_D_ITEM_MAP
with a reference to a purchase order for the grouping hash that is
specified in the message short text.

System Response

No update operation takes place for the given hash key and the program
continues.

How to fix this error?

This situation indicates an inconsistency between the corresponding
entries in buffer table RPO_D_ITEM_BUF and RPO_D_ITEM_MAP for the hash
key in question.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.