I'm no expert. I can tell you some things I've observed.
One is, that on some pistols, if you turn the screw down good and tight it twists the spring around and binds it up. I've tightened the screw down, see the spring pop out from under the trigger bar on one side and twist sideways. Then I loosened it up just enough for the screw to go back to a balanced (side to side) look and it worked great.
I've had the screw/spring out of a couple of them, maybe three?? I've not loctited or staked it back in. On one I remember it being tight (as if the notches on the sides of the screw head were still rubbing the metal displaced by the original stake job) as I screwed the screw back in. On the Pre B CZ85 I just vowed to keep and eye on it every time I cleaned/lubed it and I never noticed it trying to turn loose either. As they say, your mileage may vary.
I've read, right here, that sometimes a magazine will interfere with the legs of that spring. Remove the slide, look down in the frame/magazine well and insert a magazine (I'd try several) and see if any of them make contact with one/both of the spring legs. Just to be sure.
I've seen at least one trigger bar with little to no groove in the bottom to help hold the spring leg in place. I've read, here again, one or more forum members say they had to cut deeper grooves in one side or the other of a trigger bar to insure the spring stayed in position. I thought about doing that on mine. Tried with a small file, to make the groove deeper, gave up after not much progress and then just stoned it some trying to smooth out what little groove there was (must be some hard steel - or I had a sorry file).