User has set the Project PO # for a project, but it does not reflect on the existing invoices of the project.
This is the expected behavior in BQE CORE. Any changes you make to the Project PO # field of a project are reflected on the new invoices of the project and not existing ones. If you want the existing invoices to display the PO number, you need to delete and re-create them. Check CORE Help Center for details.