I remember you had tried the Winchester Silvertips without any problems. I know they are hard to find, for sure. I'm just thinking, with all the ammo you've tried, your R9 may have dreck and all sorts of stuff, lodged around the firing pin, and around parts that make it work.
Are you letting the R9 cool down between magazines? That could affect the fte. Just some thoughts.
As I've mentioned before, I started with Winchester Silvertips and have never tried or used anything else. What works, works.
Good luck in resolving the problem.