I believe the computer core fragments have been accidently dropped from the loot table. I have been running the Defense Contract mission every day for just over a week on 5 different toons, (2 feds, 2 klinks, and 1 Rom) and have not got a single one on any of my toons.
Ok then Still no luck with core fragments and I've been running every day on four toons without a single core fragment dropped, even by the law of probabilities I should have had at least one fragment drop by now.
I'm not sure if they are a thing of the past since I've still got several core fragments in my bank obtained before the problem started, but I'm just not getting any more. So far the only other two reasons for doing the mission from my point of view is the dilithium reward and the Deuterium surplus (Well I go through the stuff almost as fast as I do torpedoes). But like you say it would be nice for one of the Dev's to at least give us some feed back. Especially to those of us who are on a gold membership! But I get the feeling that they're trying to Nerf the amount of dilithium we can farm in a day. But I've noticed recently that not all the items that they fix are listed in the patch notes (The D'Kora comes to mind)