Just bought a Ruger EC9s to carry in my pocket when walking the dog. Quite soft shooting, great trigger and very accurate. I did have a 3 or 4 instances of slide locking back with rounds still left in mag independent of rounds left. I think it was all grip related. Can it be another issue? The slide release was impossible to push down to chamber a round the entire time but sling-shotting worked every time and was easy. I also think I was applying too much rearward pressure to the gun during those shots.

-whisky

Small guns greatly increase the likelihood of your hands inadvertently activating the slide lock lever.

Shoot it one-handed to see if the slide still locks back randomly, which would indicate it may be something else.

Otherwise, you'll need to adjust your grip. With my big hands and my tiny Kahr PM9, I had to adjust my two-handed grip to keep from bumping the slide lock and dragging on the slide.