I had a huge issue with a grey frame gen4 glock 19. I had changed connector and all the springs prior to shooting it lighten trigger pull. Thought id got a bad batch of springs so i took it all back to stock springs. Same issue. Fire the first round and never on the second. Seemed to be not resseting the trigger. I even switched back to a gen3 firing pin assembly i had. Still same issue. Got pissed. Cleaned the entire slide assembly with alcahol and reassembled. Once again same issue. I could eject the round and put it back in the chamber and fire it perfectly. Using monarch ammo. Winchester white box cured all my problems.....
I really don't mean to embarrass you here, but your problem was not that you got a bad Glock, a bad batch of springs, nor was it a bad batch of ammo that you used. I'm 99.9% sure your problem was that you put it back together wrong. What I am saying is I'll bet that the spring on the slide lock lever was on top of the locking block pin, not under it as it should be. I'm betting what you did was put the trigger pin in first maybe, instead of the locking block pin. The locking block pin has be the first pin you put back in. That's because the spring on the slide stop lever has to be installed so that that spring is underneath the locking block pin or else you will have a single shot gun. Once you have the locking block pin and then the slide lock lever in, then you put the trigger pin in to hold it all together. I promise you; if that slide lock lever spring isn't under the locking block pin, you will darn sure take a long, long time going through a box of ammo at the range! And you're gonna get real tired having to feed it one at a time. Oh it will fire, one round at a time, but it won't reset.