So, I posted this on Nate's topic also, same situation.
My Taipan Vet 2 did the exact same thing. Bolt wouldn't come back all the way 3 out of 10 shots, I had to pull the trigger and then it came back fine. The sear itself was too sensitive. I adjusted the sear and that was it. It's been perfect for the last 3000 shots. I suspect the same is with Nate's FX. The trigger is adjusted so that it performs near perfect, but sometimes a tweak is needed to make it reliable. Adjusting the sear on my Taipans trigger worked and did nothing to take away from how great the trigger still feels. Play with the adjustments just a little, you'll learn how to get the settings you want and eventually you will figure it out. It's not broken, it just needs tweaked s smidge.
My bolt probe set screw doesn't seem to be lose, and I don't believe that Nate's was lose either. If the sear is too sensitive, it seems that it can reset itself upon firing. If this happens, when you pull the lever back and it stops about 2/3 the way back, then you pull the trigger and hear a "click" and then the bolt is able to be retracted all the way, it's the sear. Obviously if the bolt probe does not retract when you pull back the side lever and the probe seems stuck, that probably indicate a lose set screw. Maybe there are 2 problems here...