I just did this quest the same way, chose to destroy the spice and did not get the "Underworld Influences" Codex entry. This one used to work before the update to the way Heroic Missions worked. Before you got the entry upon completing the quest by talking to Gizmel. Now the quest completes automatically as soon as you're done talking to the droid - you don't get a chance to talk to Gizmel, so we don't get to the point where the codex entry is granted. This needs to be fixed - as well as any other Heroic that grants codex entries in a similar manner.