Well, that makes me think checking out that spring tension on the slide stop is more important, too.
That spring actually sticks down into the hole a bit between the outside layer of frame and the inside layer. If there's a rough spot in there it may be causing the spring some drag/friction issues. Or the spring might not even be in the right place.
This is my CZ75 Compact modified to use a CZ85 slide release lever set up. On the right side of the frame you can see the thin frame section where the slide rail rides with the thicker section farther to the left. The slot between they is were the spring sits that maintains pressure on the slide stop shaft to keep it in position so it doesn't move and lock the slide back. The spring fits into that notch/shallow slot in the top right side of the slide stop shaft. You can see that long spring in the picture, too.
With no slide on the frame, if you put your slide stop in is it loose/floppy or solid as a rock and does it pop back into the normal position if you let up on it after pushing the slide stop lever down? That spring should keep it from being loose/sloppy and make it pop quickly back into it's normal position when you, or the magazine follower isn't pushing it upwards.