Looking at my LC9 (340-7xxxx, 2011), the angle on the notch goes 'down and forward'. It obviously was never intended to lock the slide.
Yours is different as its angle is 'down and toward the rear' - apparently to snag the safety and lock the slide.
I'll second getting Ruger to look at it. They will make it right and that's just one reason why I buy Ruger.