I still maintain it's trigger bar loop needing adjusting.
If you look at the video posted above by thecatch8, you can see at 4:26, that if he depressed the trigger it wouldn't drop the sear, but if he held the trigger down and lifted the slide, it would release the sear.
This could also be happening with the safety. When you're depressing it, it could be lifting the slide just enough to drop the sear.
-edit-
I'll try to explain my reasoning.
If you open the trigger bar loop a little more, you are lessening how far the trigger must travel to drop the sear, also adjusting how far your reset is.
Right now, if you short stroke your reset, it may or may not fire. If you open up your loop, and short stroke your reset then, it just won't fire, because you haven't actually caused a reset.
You basically have a trigger, right now, with zero over travel, and it's causing you problems. You actually NEED some over travel in your trigger system to eliminate what's going on right now.
Either way, if you do send your pistol to S&W, I would remove the apex parts, as they will, adjust your trigger correctly, and possibly not send your apex parts back. *It's happened before.*