Won't go bang when I pull the trigger

Howdy everyone. Just bought a new M9-A1. Couldn't wait to play with it and take it apart. It was very dirty inside as it came from the factory. So I removed the trigger group and dissasembled the slide including extracter and firing pin. I never touched the trigger group, just cleaned it. I did take the firing pin spring out and take the weight and spring off. Look for burrs, etc. Now while dry firing and practising trigger reset, occaisionally when I pull the trigger all the way back the firing pin is not releasing. And if I am not mistaken there is a double click as the trigger returns to the forward position. What did I do wrong?

Follow up......I've experienced it quite a lot now and can describe a little better. I pull the trigger, the gun releases the striker,hold trigger back while racking the slide, then release to reset, pull the trigger again and it goes back but doesn't fire. I then have to either re-rack the slide or I can push forward on the trigger and I hear a loud click, then it will fire. Is it not resetting? not picking up the striker?

Follow-up....
Yes it was picking up the striker but it was not resetting. I dissasembled the trigger group and basically cleaned and polished everything. Had a lot of rust colored junk in the sear pocket where the trigger bar fits in. Put it all back together and it works better, but still fails to reset 1 out of 20 racks. Was 1 in 3-5 before. I did notice it works fine as long as I rack the slide all the way back and let it drop. I was racking 1/2" or so before. Can you not do that with a Steyr? My Glocks work just fine doing that. In fact you can just rack it a 1/4" until you hear it click and it works every time.