I have a P-9 that was not reliable when first purchased. Sent it back to Kahr, and it came back reliable with standard velocity rounds, but is not so happy with higher velocity. It is on my list of things to look into (as in complain to Kahr), but haven't done so yet.
I use the term velocity rather than +P because in chrono'ing the ammo I was using, I found there were some standard pressure-rated rounds that had higher velocities than some +P labeled rounds. My pistol did not like the higher velocities.
Don't know if this my info on a P-9 is helpful to you with your PM-9, but there you go.
elb