Operations
Materials, labour and overhead, and the three places the number usually goes wrong. If labour is booked separately from the product, your product cost is not your product cost.
Accounting
A long close is rarely a staffing problem. It is a list of things that were allowed to go unresolved during the month, collected and resolved at the end of it.
If you cannot explain how an item cost was calculated, you cannot defend the margin that depends on it. What moving average actually does, and where it goes wrong.
Two numbers that must match and usually do not. The causes are few and specific, and each one points at a different missing control.