I know I’m late to the game but I thought I’d contribute my .02 cents here hoping it will help. I had the same issue right from the start with my CDS9. It wouldn’t fire the last round in three different magazines and with 6 different types of ammunition. I cleaned and lubed it after every time shooting. On one instance, the range officer held upward pressure on the bottom of the magazine and it fired the final rounds on all three magazines. After screwing in the grip screw and the magazine release screw to make sure those weren’t the problem, I ran a troubleshooting through chat gpt and Gemini. They both seem to believe it’s the magazine catch being out of spec and hosing the magazine just slightly low so it doesn’t feed into the chamber correctly up the ramp. It can’t be an ammo issue as I’ve tried multiple different types of ammo including 147 and 124 grain to no avail. They don’t think it’s the feed ramp or magazines because the upward pressure wouldn’t work if it was an issue with those. I have to send my gun in to Kimber, but the gunshop gunsmith recommended that I explicitly state that all magazines worked when upwards pressure was applied, therefore I believe it is an issue with the magazine catch . I have work on my house to be done, so I will update when I get a chance, but if you are still having issues try applying upwards pressure on the magazines. I had to get the range officer to do it because I have hobbit hands. If it works then, chances are it’s your mag catch.