While there are some variances from gun to gun, Remington has told people that the RP9 likes hot ammo.I would try what is suggested by Cross K and Mark G, but I also would change up your ammo.

Hopefully you cleaned the firearm after getting it new before firing it? If you fired it very much and had not cleaned it - the powder can build up being clung together by any oil/lubricant on the firearm when you first received it. Try cleaning it up then try Mark G's plunk test and see how it goes. --CK

Ammo will affect the round seating. Take the barrel out of the gun and do a "plunk" test. This involves dropping the ammo into the chamber to see if it will easily go in and then rotate freely with your fingers. If the ammo does not drop in freely you have an ammo problem.