I agree with many of the statements and sentiments expressed so far ...
Kahr's go through recoil springs pretty quickly if you shoot often. Follow the factory recommendation on how frequently to replace them, especially with the .40 S&W.
Kahrs seem to like sufficient lubrication, liberally sufficient.
Reduced slide mass, increased slide velocities, short slide travel and a high pressure, hard recoiling caliber ... and then, you're adding a polymer frame to the mix. Don't mistake that using a Weaver 2-handed shooting grip will completely prevent a grip stability issue from being involved. Granted, it's less likely when shooting 2-handed, but I've seen some folks manage to carry it off.
Lock your dominant wrist & forearm.
A lot of Kahr owners seem to experience functioning issues until they're past the 200-round minimum break-in period. Big surprise that Kahr recommends a break-in period, huh?
Although, I helped a follow break in his MK40 last year, and his pistol exhibited no functioning issues right out of the box. He brought it to the range still NIB, unfired, to qualify with it as a Secondary & off-duty weapon.
The range was pretty slow at the time, so I offered him the time and free ammunition to fire approx 150-200 rounds, including a qualification string, if he was interested. He was ... and between him & I, we 'broke in' his MK40. Snappy little pistol, and that's with the steel frame, too. As I recall we were shooting mostly Remington Express 180gr JHP's at the time, which have a rather large nose cavity, but his MK40 ran through all of the rounds without a single malfunction. None at all.
The next time I saw him, for another qualification, he said his MK40 was still functioning perfectly reliably, but he was having issues with recovery and controllability ... one hell of an anticipatory flinch ... apparently caused by the .40 S&W caliber in the small pistol. Personally, I find the G27 to have better controllability, for me, than the all-steel MK40. Odd, but there it is ... I'd have no interest in a MK40, myself. I've borrowed a K40 that was much better, overall, except for the weight. It's always something, you know?
I've seen a couple of Kahr polymer .40 S&W's come through the range. One of them was a PM40, I believe, and the owner said his pistol had been functioning fine. It exhibited no problems as he completed the course of fire. We didn't have time to discuss his experiences since first buying the pistol, though, so I have no idea how it functioned for him when it was new.
The other one was a P40, and the owner said it was good pistol, and he liked it ... but that it malfunctioned a lot. He demonstrated that tendency on the range, too. I suggested he return it to Kahr for examination, repair or whatever ...
Clean your PM40, lubricate it well, lock your shooting wrist & forearm ... and try another 100-200 rounds of quality ammunition. If you still have functional reliability issues, beyond the 'break-in' period, call Kahr.
Of course, you do realize that once you've fired enough rounds to have confidence in it, it's probably going to be time to replace the recoil spring, right?
Let us know what happens. Call Kahr anyway, and see what they say. At least let them know that you've exceeded their recommended 'break-in' round count and still have some potential concerns.