Is this for dry goods or liquids? Is the sieve intended to filter product to size, or merely a catch for FM? I ask because I started my career in a spice/vegetable milling facility, and we used sifter boxes to achieve the ordered powder or granular sizing, so oversized product would get kicked out to rerun through the mill and too fine/small material would be separated to go into other product. Because of that, we couldn't state the sifting process was applicable to FM, especially as it came in after milling.
Ideally, I'd say the magnet first, sieve and MD last if the hazard you're concerned with is metal FM. If you're concerned about other FM as well in this bulk product, the sieve might become a CCP.