Have you run Day End Processing in OE? Have you shipped and invoices any quantity of this item in OE since your last Day End? If so, then costs and quantities are not guaranteed to match in inquiries and reports specifically in the FIFO lot costing buckets. Perhaps that 'missing' 5 lbs has been recently shipped.

To check this out, use the Column Editor on your Edit Items or Items w sales/costs grid and add the field 'Qty Shipped not Costed'. Any item with a non-zero qty has been shipped in OE since the last OE Day End.