https://userapps.support.sap.com/sap/support/knowledge/en/3750455
3750455 - Address number removed in PO after editing Delivery Address tab - SAP ERP & SAP S/4HANA-...
When a Purchase Order (PO) is created, on 'Delivery Address' tab the 'Address' number (ADRNR) is determined automatically. After changing any field manually in...