While shooting my CZ the other day the hammer hung up in the cocked position and wouldn't drop when the trigger was pulled. After I unloaded it I managed to get the hammer to drop, then detail stripped it. Everything looked normal so I gave it a good cleaning, lubed it up, and proceeded to put over 100 rounds through it without an issue. Then yesterday the SO was at her CHL class and halfway through qualifying it did it again.

I'm sitting here looking at it and I've noticed that if you cock the hammer back using your thumb that sometimes the sear will catch the second notch on the hammer instead of the first, resulting in some difficulty getting the hammer drop. Only thing I can think of is that I might need to replace the sear, which I was planning on doing anyway with an adjustable Cajun Gun Works sear.

The gun has a couple thousands through it, which isn't much I know.

Second notch? There's only one notch on a SA hammer.

Usual culprit for not being able to drop the hammer on a SA would be a misadjusted overtravel screw (that is, the screw too far out, not allowing sufficient travel).

Your right, there isn't a second notch. What's happening is the hammer is going back far enough to allow the sear catch on the back side of the hammer.

Had the same issue with my SP-01.  No problem with DA, but it wouldn't drop the hammer in SA.  I could see that the hammer would go back a tiny bit when the trigger was all the way back, but the sear wouldn't disengage.  Got a shipping label from CZ, sent it to them and they got it done in about a week.  I got it back with a note on sear polished and adjusted.  It's been 100% ever since.

That shouldn't be able to happen. The hammer should bottom out on the frame before coming back that far. Something is definitely quite wrong.

I'm replacing the hammer and sear with CGW parts. I'll post an update once I have them installed.