yes this is common even with the glock 45 small frames got to lock your wrist and get a thumbs of the frame grip,interesting on the firing pin???I picked my new CM45 up Thursday but didn't get it to the range yet. I DID, however own a PM45 at one time and shot it so I know what you are experiencing. I would say that I really don't think you have a recoil spring issue. I would say that you have a wrist issue. Not that you have any limp wrist issues in general but these things are so tight, light and have such minimal margin for error in their cycle that ANY flex in the wrist is prone to absorb enough of the action to allow the slide to lock back.
Similarly I would consider the possibility that your two failure to fires might have been from the slide not being fully in battery. I've had experiences with Kahr 45's both CW45 and PM45 being unable to come fully into battery on 230 grain JHP ammo of some brands. Mag Tech and Hornady come to mind.
One thing I HIGHLY recommend for these guns is a wrap around grip. These little 17.3 ounce (+2 for magazine) 45 ACP's are a bear to shoot much. My PM45 rubbed a hole in my hand the first time I took it to the range. I use a bicycle inner tube to make custom size wrap around grips for all of my pistols now. $5 for 20-25 grips is hard to beat.
Also, did you send in for your free magazine?
http://www.kahr.com/MagPromo2014.asp