Bin being assigned on Item Fulfillment is not the Preferred Bin of the Item despite having enough quantities

Summary: NetSuite will auto-assign bins on Item Fulfillments and/or NetSuite does not pick the preferred bin when it auto-assigns preferred bin on Item Fulfillments.

Solution / Reasoning:

If the preferred bin quantity can cover the transaction, the preferred bin is used.
If the preferred bin quantity cannot cover the transaction but another single bin can cover the transaction, that bin is used.
Otherwise, you must distribute the quantities among bins that contain the item to cover the total quantity.