AOD is 'always on display'. I had same issue with the gmail app not giving notifications. Tried everything to get to show up. Ended up just going back to aquamail.
This feature was one of the reason I wanted a note 7... I have tried everything including what kjgilligan suggested, but it did not ask about an update. Still just pins to an 'icon' rather than pinning to the actual 'always on' screen.