What I thought was a light hit turned out to be the hammer falling on a spent case because the cylinder was not rotating.
This would occur about 1 out of 15 pulls or sometimes less.
This is a 6 month old 637 PC J Frame. My question is this a hard fix or can a local smith handle it ?

the hand is missing one of the ratchet teeth occasionally it sounds like. With it being only ssometime , that could be a number of things. Damaged tooth, damaged hand or as simple as the gunk in there that sometimes gets in the way of the hand moving forward. If you are well versed in the inner workings of a revolver, it wouldn't hurt to look. If not, call s&w and they should remedy it.

In double or single action? Once after shooting a bunch with a semi-auto, I was target shooting with an old Model 19. I shot a round and while still holding the trigger back (as if it was a semi-action pistol) I cocked the gun to shoot again in single action. With the trigger back though the cylinder does not rotate. Oops.

If you were shooting in double action - Qballwill seems to have the answer.

Don't know if this will help, but make sure the sideplate screws are tight. I recently had them loosen on a PC 442; this played hob with the DA. There were more problems with this PC gun than Carters had Little Pills.

Kaaskop49
Shield #5103

Of course S&W will eventually make it right at no cost to you other than time, but a local gunsmith can probably fix it in a jiff for relatively little money and you can get back to shooting lickety split. It wouldn't hurt to at least bring to a local shop, where they'll probably crack it open for a quick peek and let you know for free whether it's an easy repair.