It was always surprising to me how people could have difficulty racking the slide of a pistol. I was blessed with size XXL strong hands. They come in handy, except when buying gloves. But the past month or so has been an eye opener. I've got a problem with my left hand. Can't pinch grip anything with my thumb. Seeing the doctor soon. I've overdone it recently cutting down dead ash trees on my property, so hopefully it's just temporary inflammation. It's given my a whole new sympathetic view towards people who struggle racking a slide. Luckily I carry either a 642 or a BG380, which I can still rack.
To the OP - I'd do what others have suggested and try to compare yours with other Shields. I'd think if yours came with an overly stout recoil spring it would have affected gun function.
One other thought. Do you have other pistols, and are you able to rack them OK? Just to eliminate the problem being your grip, as opposed to the gun.
Good luck,