for me and mine I had to make sure the buffer was oiled with a sheen of oil, otherwise I experienced stoppages, usually the case spinning and coming back in.... like i was not getting enough bolt speed.
my .223's I could run dry as can be.... the 9mm seems to like to be run a little wet for some reason I cannot fathom. Other then that my gun has been very consistent and runs like a top both with my borrowed uzi mag and the RRA 10 round mags, bolt hold open works super with the rra mags.
what kind of buffer are you using in the 9mm.... a proper 9mm one or ??