Did you eject a live round when you racked? If not, you did not have the mag seated properly. If you did, you may have a problem. How many rounds through the gun? after 1000 rounds or so, you may have enough debris inside to interfere with the proper functioning. I always recommend a good detail clean every year or 1000 rds, whichever comes first.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball