Why isn't the supplier showing up when creating PO?

Summary:

Supplier has multiple site assignments to multiple client BU's. Purchasing is selected for both sites and BU's. Supplier is only showing up during the PO creation for one Purchasing BU and not the other. Why is this happening?

Content (please ensure you mask any confidential information):

Supplier

Site A - Client BU A - Purchasing, Primary Pay

Site B - Client BU B - Purchasing, Primary Pay

Having this issue in TEST and PROD environment and happening for multiple suppliers.