CMC trigger issues, need advice

I'm going to assume that the trigger was installed in AR platform. I'm not positive but a couple things are likely. One is a weaker hammer spring, nor exerting as much force on the firing pin. Another is milspec primers with a harder promer cup that is harder to ignite. Could be a combination of things

I have 3 identical CMC flat trigger units installed in 2 AR15's & in 1 AR10. Haven't had any issues to date.
2 of the triggers were purchased 6+years ago, 1 was purchased 2 years ago.

Try a different brand/batch of ammo & see If problem persists

I also have a gaggle of McCormicks.
Love them.
How difficult were the pins to install? Sometimes the receiver holes don’t match well and cause some binding that can suck energy.
The detriment and benefit of cartridge triggers, the precise location…

I've had that exact same issue. For me it was the Winchester primers in that 350 FMJ ammo. Try a different brand of ammo to see if the issue persists. I can usually get the ammo to fire on a 2nd or 3rd attempt, but mostly I quit buying that ammo because it sucks and my partner reloads ours anyway.

If that's the only ammo available to you, I recommend shooting it in a lower with a stronger hammer spring. The 350 legend AR I hunt with has a single stage CMC trigger, and I use either Hornady interlocks or similar handloads. Good luck.