Product missing in customs declaration

Hi Gurus

I created a purchase order with some line items in ECC and completed an Inbound delivery(Shipping notification) completed the delivery and able to see all the line items under import legal control for a given PO number and ASN number but one line item is missing while creating the customs declaration and also not able to see the PO number under the reference Tab.

Please suggest what could be the reason and also process to resolve the issue.

Thanks & Regards

Karthi