MRP Generate Planned Jobs is not returning an expected suggestion

The best place to start investigating this problem is in the Stock Status screen for the item in question.  To access it, go to (Inventory > Stock Items), select that item and click the 'Stock Status' button.  Within the Stock Status tabs, you'll see what's contributing to the supply/demand for the item in question.  A very common reason for not receiving expected suggestions is Planning Period.  If you have demand that falls outside of the item's Planning Period then MRP should not be suggesting a Job to manufacture the item yet (until the demand comes into the Planning Period).