So I figured it out. It wasn't anythng mentioned so far. It was some Loctite that had dribbled down from the CGW sear adjustment screw and wicked onto the sear pin, causing the sear to bind ever so slightly. I took the pin out, degreased it and polished it once more, re-installed and the problem went away.
For a while it was a real puzzler though, because the hammer would lock back on one cycle and fire, then on the next the sear would not engage the hammer. Then the next cycle (cycling the slide or thumbing the hammer back) it would work, back and forth like that with every second try working.
While I had it apart I tapped the hammer pin detent hole for a 4-40 set screw so I won't lose that detent again. Pretty easy to do in aluminum and took just a couple of minutes.
Now I am looking at the safety and thinking about trying to improve the solidity in both the safe and fire positions. It is pretty sloppy as it came.