Note: If you have part traceability turned off then you will be unable to search by supplier using this report.
The supplier on the report is the preferred supplier, not necessarily the actual one.
The supplier range in the report filters looks for the supplier that the batch was actually received from. Check it against the export clicking 'show batch & supplier', to show the specific batch that was received from the specific supplier.
If you are running the report against any suppliers that are not approved or have exceeded their expiry date, the stock won't show on the part usage report because it is from a different supplier and batch.
If you would like to delve into this further, try the part usage report with different suppliers until some part info shows and then compare this supplier with a supplier that does not produce any data. My inclination is that the suppliers that don't work are not approved or exceeded their expiry date. Check this by selecting the following:
Purchase
Supplier Maintenance
Approval tab
Check approval and expires: field and if uses approval method field
Also, there is a report which generates data for purchase order goods received by supplier. Please complete the following steps:
Select Purchase.
Select Purchase Order Receipts Menu
Select P/O Goods received by supplier
enter date range and supplier code and click Export