Bill--
The forward edge of the ejection port and the forward edge of the barrel hood would wear each other. The result was a failure to return fully to battery.
My PM9 suffered from this shortly after I bought it. I called Kahr and talked to Dottie. She confirmed that mine was in the affected S/N range. I sent in the "top half" (barrel, complete slide and recoil spring assembly).
Kahr replaced all of the above within about a week. It has worked perfectly ever since. I carried it for a bit over three years, and still own it. I've been carrying it's big brother (P45) ever since.
Best, Rich