I registered here to post my similar experience to the OP.
Just bought a Kahr PM9. I absolutely adore this pistol. It is exactly what I have been looking for for many years, but never took the time to research and acquire.
Got it home, took it apart, familiarizing myself with the parts, put the slide on to check fit and workings, and . . . slide now not removable from receiver.
I have a different opinion than the OP. I made the decision to put the slide on without the other components installed in the slide (spring, barrel), and so I take responsibility for causing the lock up. Can't blame the gun manufacturer for that. Sure, my glocks and other semis don't do this, but why should that matter. A bit angry with myself, I begin fiddling with it. I determine that the spring loaded nubber sticking out from the center, back of the slide is hanging up on something, preventing the slide from moving forward, off the receiver. I'm quite sure that nubber is the technical term. In any case, I tried various techniques to get the nubber to ride up over whatever it was catching (inserted feeler gauge, various amounts of pressure, and so on). All to no avail. I tried mag in, mag out, pull trigger, and so on. No dice. Close to giving up and bringing it to a gun smith, I stumbled upon the following technique, which worked:
In the "stuck" position, the slide is rearward on the receiver, in "normal" position or further back in what would be the mid-cycling position. I moved the slide forward until I felt the slide spring inside the slide start to compress because the nubber was catching something in the receiver, and then, with that spring slightly tensioned and applying forward force (not much) to the slide, I pulled the trigger. The action of pulling the trigger with forward pressure allowed the slide to come off.
If you look at the part that projects upwards from the receiver, it's shaped, in profile, much like a V, which is why, I believe, simply holding the trigger and then applying pressure forward on the slide did not work - with the trigger pulled, the nubber on the slide simply ran into the back leg of the V.
The key step, for me, was applying force to the slide forward first, which caused the nubber to hit the "front" leg of the V, thereby placing the nubber between the front leg and the back leg. That is, in the crotch of the V. By pulling the trigger, the V pivots on its point, and by continuing to push the slide forward, the number moves forward over the front leg of the V, which has pivoted downward.
If this post saves any person from a trip to the smith, then I'm happy.
Also, love the PM9. Great, small carry pistol. I had a berretta Jetfire (380 auto, IIRC EDIT - looks like 25ACP - been a long time, LOL) and a Ruger LCP. both of those were abysmal. The jetfire never was able to cycle a full mag of any ammo, and the firing pin broke at some point before 40 mags were fired. The LCP cycled about 1 out of every 2 mags properly.
Everybody has their preferences for a gun.
My first commandment for a gun is this - Thou shalt bang upon the pull.