I took my 43 to the range yesterday afternoon. The first two mags didn't have any issues- shooting it actually felt pretty good as was the accuracy. Part way through a third magazine, I fired a shot that caused the action to cycle properly and the trigger reset to the cocked position however the trigger would not pull to the rear to fire, even with remedial action (tap-rack-try to pull, nope). To rule out an issue with ammunition I also tried to dry fire it. No joy. When I got home, I was about to manipulate the slide and get the trigger to release and disassemble. Field stripped, everything seemed to "be right"- in both the lower and upper. When manipulated the trigger set and released correctly. When pressure was applied to the firing pin safety, it moved as it should. The striker also moved correctly. Upon reassembly, it dry fired correctly.  

I followed the same (standard) lubrication procedures that I use with my many other Glocks- without issue.

Anybody have any hypotheses as to cause? Are any special cleaning or librication points that I should consider?

My best guess would be something got into the trigger mechanism and you eventually dislodged it which is why it started working again

That would definetely make sense.

Even though my rounds through it are in the single digits, I'll give it a good cleaning and lubrication then get it back to the range again. Let's see how this plays out. I have a lot of Glocks (19, 22, 27, 29, 43, 44, 48) and this really the most significant problem that I have had with any of them. A piece of debris wouldnt be the gun's fault- maybe ammo, maybe environment. Hopefully it proves itself trustworthy.

Trigger safety hanging up on the frame? Finger not square on the trigger?

Trigger (drop) safety was definitely disengaged.

The trigger safety was definitely clearing well before and after the issue was resolved.

Did you ever find any trash or debris in the gun?

Not necessarily.

I did find a couple of small pieces of debris on the counter where I got the trigger to release while disassembling it- but that was a day later. I'm not sure if those fell out of the gun or were from somewhere else.

Though I have owned this gun for a while (bought in April), this was its first trip to the range. I have not CCW'ed this gun or had it in a holster yet. It did ride to the range in a pistol case in my range bag and had been on the bench before firing (and while loading mags 3 and 4).

The trigger return spring would be the only real small part in the gun. I wonder it the retainer for the spring broke.

I had a similar issue with my G19 recently.

Somehow the trigger return spring got hung up. As a precautionary measure, I replaced the spring.

GTG ever since.