I haven't been back to the range (yet - next week I expect) but I have stripped the gun and cleaned it. I even took the bolt off the rails as in the video and photos in the forum (but not in the manual). Soaked the bolt & blew that whole area out with compressed air. Light oil is now only on the rails - it's no where else on the gun. (Take that back, I used the same wipe to wipe off the bolt spring and guide above.)

Hammer pin is back in position - I'll keep an eye on it. Hammer and trigger springs are inspected - not broken.

On closer examination I did feel a slight bur on the very end of both rails. It seems like they're metal rails with a polymer coating and on the very end a bit of metal is exposed and that seam is not perfectly smooth. I haven't sanded it (yet) but may pull it back out and do that before i head back to the range. It wasn't a big bur, but I could feel it with my finger once I was looking over everything with a fine tooth comb.

Thanks much for all your great suggestions. I'm feeling good that any one of these items could have caused it & with your help I think they're all resolved. I'll let you know...