I registered just to reply to this. ( I looked when this happened to me and didn't see much out there)
I bought a Shield 9mm about a 2 months ago. It was between that and a Glock. I chose the shield.
My first time to the range, at about 170 rounds I had the exact same thing happen. The slide was pinned back, all the way back, after ejecting the shell, it really freaked me out. I dropped the mag, and got it to where I could remove the slide and checked the spring. After visual inspection, everything looked ok, so I put it back, and sent another 20 or so rounds through it before the same thing happened again. This time I slammed it forward on the wood paneling of box I was in. I continued to fire it, and after about another 200 rounds I decided to leave ( no more problems after that last time). Also, one thing I can say is that it racks much smoother than when I first shot it.
I have since sent another close to 800 rounds through. Only one issue since, just a round that didn't fire on first strike. Second run through was fine.
Later on, I checked the S&W forums, and this is apparently not unheard of, a lot of folks seem to send it in and have the spring replaced, and some It could be operator error. I personally have always owned Sig handguns, but this was to be my daily carry and I wanted to try something different. So having this happen not only had me shocked, but a little angry that I didn't go with my first instinct which was the Glock.
I'm not trying to start any religious debates (gun is better than that), this is just one person's opinion. I haven't had an issue with it since. But unfortunately it may have ruined trust for me.
But yeh, if you are getting here from a google search, just check that the spring is seated correctly or you may have to send it in to the MFR. Reliability is paramount, so I would definitely make sure that your specific weapon is trustworthy before carrying.