That spring on the right side (inside) the frame should be moving the slide stop into the correct position to release the slide when nothing (the follower on an empty magazine for a slide stop that is made correctly) is pushing upwards on it.
There have been a very few instances of the slide stop end making contact with the bullet of the top cartridge and pushing the slide stop upwards into the slide lock position.
Is your spring intact and in place? With no magazine in the frame and the slide forward push the slide lock lever up and feel for resistance. It should resist your finger pushing it upwards and immediately pop back to the down position when your finger releases it.
If it's a bullet contact with the tip of the slide like inside the frame you can see that by removing the slide (like field stripping it to clean), inserting a loaded magazine into the pistol till it locks in place and looking at the slide stop to see if it moves upwards and/or makes contact with the slide stop. It should not.
I forget (been years) which combo of parts this was on one of my pistols. I swapped parts from one to another and saw this. A couple CZ P07's or P09s.
Here's a picture of the two slide stops side by side.
Neither of these may be the issue you're having, just a couple possibilities.
Good luck with it.
edited to add - see those grooves in the slide stop pin on the right side? That's were that spring mentioned first rides. The spring pushes down on the pin and when the follower pushes it upwards at the back to lock the slide back the spring isn't sitting flat in that groove anymore. Once the follower is no longer pushing the slide stop up at the back there the spring will force the slide stop shaft to rotate to the point where the spring is once again flat in that groove.
