good ideas here. I've been working the safety as I draw the pistolI'm 60+ and have little trouble with my safety. Perhaps some rust inhibitor or cutting oil got in the safety area and gelled, shoot some Kroil or Liquid Wrench in there work it in. If that fails there may be a burr or metal filing binding the safety. Try one or two other Shields for comparison, if your gun is markedly different send it back to S&W for repair. If your safety feels the same, just work it on/off a couple of hundred times. It should smooth out.
BTW if there was an enhanced safety lever on the market I would buy it right now.
and it is getting a bit smoother. I'm also using the front part of my thumb while temporarly adjusting the grip. With practice, it is working out pretty well and seems to be totally reliable. The shield is really a very nice CCW.