I'm sorry to hear about the OP's problems with his Shield. Hopefully the repair fixes the problem and your gun runs trouble free now.
Reference stiff springs and hard to manually lock the slide open...
As guns get smaller and more compact, adjustments have to be made to help soak up the recoil. When the slide mass is lightened the recoil spring tension is usually increased to accomplish this. These heavier springs result in a gun which can be hard for some to manipulate. The Shield is a prime example of this with the spring tension really ratcheting up as the slide reaches the limit of it's rearward travel.
Because of this, I've found my wife and daughter prefer semi guns with more slide mass and lighter springs. Their favorites are the sub-compact and compact GLOCK 26 & 19. They prefer these guns because the slides are wider (easier to grasp & more mass) and the springs are lighter and therefore are easier to "rack" than my Shield's slide.
On another note, they really dislike ALL of my J frame snubbies, especially the aluminum framed 642. They find them hard to hit with, have very heavy triggers, and snappy recoil when compared to their favorite 9mms.
Sometimes the guns which seem small and perfectly sized to fit into the purse while at the counter aren't as well suited for some shooters once you get them to the range.
The ladies in my house accept the slightly bigger guns to get an action they can manipulate. That leaves the J frame snubbies and Shield for me!
Edmo