Tuning the slide stop on the Kadet Kit has many factors that must be perfectly balanced for proper lock back. I have my Kadet Kit fitted to a P-01 (alloy frame) and more recently an SP-01 Phantom (polymer frame). To test the slide stop, you need a field stripped frame and a Kadet 22LR magazine. If you have an alloy or polymer framed CZ75, you will find that the P-01/SP-01 9mm slide stops' inner lugs are way to short to contact the Kadet's 22LR mag follower. The solution is the PCR slide stop which has a longer inner lug. Since it could cause 9mm bullet clearance problems, the PCR slide stop should only be used for the 22LR kit. Save the regular slide stop for 9mm use.
When I got my PCR slide stop, I found that it indeed had an inner lug long enough to contact the follower, but the magazine spring was too weak to overcome slide stop friction and the frame's slide stop spring. One thing that helps some, but does not solve the problem, is to clean out your Kadet mags. After 1,000 rds or so, the red plastic follower gets caked with 22 grit that impedes follower upward motion. Removing the base plate is not easy. I used a plastic or wood pusher tool to press in the base plate button while simultaneously pushing the base plate back. The first few times it will feel like it won't budge. I place the mag front side down and press down hard on the metal mag body using my palm (pushing in the button at the same time). Once the mag is disassembled, clean it with a test tube type plastic bristle brush. Don't over lube as that will just attract more grit. Brush the mag follower as well. While I was at it, I gave the mag spring a bit of a stretch (1" to 1-1/2" longer). Don't stretch it longer than that or it can be hard to get the spring back in the mag. Reassembled, the mag is now smoother and has more upward follower push.
This probably won't fix the problem but will make it more reliable once you address the other factors.
The slide stop is retained by a spring in the frame that also exerts downward force on the slide stop. With a 9mm magazine, the mag spring has more than enough force to overcome the slide stop spring and lock back the slide after the last round is fired. However, the Kadet kit mag spring is generally too weak. One could remove and reshape the slide stop spring and fix the problem with trial and error. However, as the 9mm and 22LR require different amounts of slide stop spring pressure, one must strike a careful balance with this approach.
I decided to leave the slide stop spring alone and address the PCR slide stop notch where the slide stop spring rests. The deeper this notch is, the less downward force the spring exerts. The deeper the back of the notch, even less downward force. If not enough downward force is exerted, deepening the front of the notch slightly can help. Using a small fine round needle file, I deepened the notch on the PCR slide stop enough to decrease the downward force. One must be precise and not angle or widen the notch. If notched deep, it can be hard to push out the slide stop, so a light bevel at the right side of the notch will help disassembly. This only deepens the notch a small fraction of a mm, but since it may weaken the slide stop, only use the tuned slide stop for 22LR use and use an unaltered stock slide stop for 9mm. Once fit properly, reblue the tuned slide stop and lube with gun oil.
With the alloy P-01 and tuned PCR slide stopI now have reliable lock back after every last round of 22LR, which saves wear and tear on the firing pin (no dryfiring). I can also allow others to shoot it without worrying that they will lose round count and dry fire. I have it tuned so that pulling the slide back sling shot style with a fresh mag or no mag will unlock the slide (retaining enough downward slide stop force to allow the slide stop to disengage). 9mm function with the stock P-01 slide stop is unaltered and fully functional.
With the polymer SP-01 Phantom, the extra friction of the polymer frame meant that I had to tune a second PCR slide stop with a slightly deeper notch to reduce downward force even more. I now have 100% lock back after the last shot, but the slide stop will not release with the sling shot method. However, it will release normally with a simple push of the slide stop lever, as one would normally reload. I tested the Phantom with hundreds of 22LR rounds, and it never locked back prematurely (with rounds left in the mag) and now always locks back when it should.
So my suggestion is to order a spare slide stop for 22LR tuning.