I Also purchased a 5" 9mm Pro about four months ago. It suffered 8-10 light strike per every 100 round. I contacted Smith and they sent out a new striker assembly. That did not fix the problem. Sent the pistol back to Smith and they stated they replaced the barrel and put in a new striker assembly. That did not fix the problem. Finally after cleaning the pistol, I tried to insert a empty magazine into the pistol. The mag would not seat completely and when I removed the magazine, the sear deactivation lever (yellow metal thingy) and a small spring fell out to the bottom of the magwell. Back to Smith it went for a second time.
When I got it back, the note stated they changed the springs on the striker assembly and the reinstalled the sear deactivation lever and small spring. It looks to me the deactivation lever could have been the problem all along. I believe it was not installed correctly and it caused the sear to be ever so slightly raised or tilted. This caused the lower leg of the striker assembly to drag on the sear, sometimes taking away the sufficient power to ignite the primer.
That's just my opinion from someone that doesn't know a whole hell of a lot.