Any update for us? I've got a 9mm (mostly RRA parts) doing the same thing. Frustrating as hell. I'm about ready to sell the damn thing.
I'm using a RRA mag block, RRA modified Uzi mags, DPMS lower, Magpul stock, TROS 9.25" barrel, and a Bushy M16 lower parts kit. I'm running this with my DIAS. I started out using the RRA 9mm buffer. Now I'm trying a DPMS buffer. I've tried Winchester WB 115-grain ammo primarily, but did try a mag worth of Brown Bear 145-grain.
The initial problem was that the gun wasn't timing right. It was functioning fine in semi, but on full-auto I was getting "hammer follow" kind of like when you have bolt bounce issues.
I had the bolt ramped.
Once I started screwing around with different buffers, I started to get some failures to eject. Now it happens all the time in semi and full-auto. I can't believe it would be the buffer causing the problem now, but I need to put the RRA buffer back in and try it.