are you using factory ammo? Ive had reloads not go into full battery due to over crimping and it was hard to pull the slide back and eject the round. If its
factory ammo I have no idea what it might be. If the round is over crimped it will cause it to bulge and keep it from fully entering the chamber, therefore not
fully "cocking" the gun so nothing will happen when the trigger is pulled. Make sure the slide is all the way forward when this happens again, if not this could be the problem. Have you tried more than one brand/type of ammo? Is the gun new?
Also, welcome to the forum from CA!