My CM9 has been flawless from the very first round fired. I wouldn't call it a break in, but rather a shake down. Because after an initial cleaning I shot 100 rounds of mixed ammo through it without a single problem. I used WWB, some old Remington UMC I had on hand, and also some Winchester NATO rounds.
I then tried it with candidates for carry ammo. Remington Golden Saber, Winchester PDX1, and Hornady Critical Defense. Again, all functioned perfectly. I have since put another couple hundred rounds through it without any problems. My final decision on carry ammo is Speer Gold Dot +P Short Barrel. Mine seems to not be the least picky about ammo.
I don't know what loading the first round with the slide stop would have to do with subsequent rounds, but that is Kahr's instructions. I also know the trigger reset is pretty long, so maybe in that instance you are not completely releasing it.