Could be a bad batch, could be your hammer spring is installed incorrectly. I would just randomly guess it's one of those 2 (my instinct would say hammer spring installed wrong)

What FCG and what springs?
Was it just an inertial FP tap or a more normal looking strike ?
Tap probably means the bolt was not closed.
Heavier hit usually hammer spring backwards or spring too light for mil ammo primers.

This is almost always a reversed hammer spring with .223 ammo. However, I did have a hammer pin back out and cause intermittent light strikes.

Agreed. Light primer strikes is the gun, not the ammo.
I just did a video series addressing these issues

Here is the first of three. I also talk more about light primer strikes in the third video.

https://youtu.be/IvTW1mHmw8g

I'll look at the spring, but I've done a number of builds, and I'm usually careful.

It is a standard PSA fire control group. I am looking to upgrade in the future.

Is the firing pin clean, no grease or dirt. Firing pin in spec.

It's clean, and I assume in spec.

I would thoroughly clean and properly lube the barrel, chamber, barrel extension area, and the complete bolt carrier group.  Double check to make sure the hammer spring is installed correctly.  Make sure there is no debris in the trigger group, like a popped primer, slowing down the hammer.

I had a similar problem a few years ago, with a primer slowing down the hammer.

First thing is to follow MILSPEC's advice and determine if the spring is installed correctly. If it is, I would recommend pulling the BCG afterwards and check the firing pin channel for any obstructions or carbon build up from your previous shooting session. Also, examine the collar of the pin and the cavity it rests in on the BCG to make sure no debris or obstructions are present. Then retract the bolt and press on the back of the pin to ensure that it is protruding within tolerances, then test for free movement. If all this checks out, make sure that it is going completely into battery each time. If it doesn't, then further troubleshooting steps will be necessary to determine why it won't

As others have stated, thoroughly clean all components, including the chamber and area inside the extension lugs, then retest.

hammer spring installed incorrectly.

If the hammer spring is right then check FP protrusion.