The External catalogue order properties for WMSADDRESSID are set to TRUE (as below description for this field) which is taking the warehouse number from the PO header as the addressID but then taking the ShipTo address details from the Delivery address name on the order. This is inconsistent.

The ShipTo address should be taken from or be consistent with the WMSADDRESSID if the parameter is set to TRUE.

The default delivery address on the purchase requisition from punchout catalogue should also default from the WMSADDRESSID (warehouse address ID) and not require a manual update. It works this way for items and on purchase orders.

Order default from docs.microsoft.
WMSADDRESSID Set this property to TRUE to use the warehouse number on the purchase order header as the addressID value in the ShipTo address for the purchase order request that is sent to the vendor. If you set a value for the FIXEDSHIPADDRESSID property, that value takes precedence over this value. Therefore, you should use one property or the other to set the addressID value in the ShipTo address for the document.

Current code:
//Header ShipTo
orderHeader.appendText('');
orderHeader.appendText('

orderHeader.appendText(this.processShipAddressId());

orderHeader.appendText('');
orderHeader.appendText(vendPurchOrderJour.DeliveryName +'');
orderHeader.appendText('');
orderHeader.appendText(this.processDeliverTo());