the worst ive had is a fail to reset after 1 round is fired. no slam fire or run away. what happened was the setscrew walked forward after about 2-300 rounds. after that i started to use locktite.
I use the second set screw to lock the first one in place. My method; set safety to on, run set screw in until it makes contact with trigger, back off 1/2 turn. Run second set screw in until it makes contact with first set screw and tighten 1/4 turn. I have not seen any issues with the screws moving.
I don't run loc-tite on mine just in case I decide on a different trigger in the future. On the JP trigger I red loc-tite the set screws as per instructions.
My issue with the piston upper is the sharp recoil, not a push like DI uppers. I think that is what caused my multiple shot problem.