[gmsoapy]

My very new Mark III Hunter has the same issue. I have not been able to figure out what it is. Definitely not a magazine issue because all 12 magazines the same and with the same magazines 2 other Marks lock back fine.

Let me know if you figure out what it is.

Redleg
Have you broken it down and gave it a good cleaning around the bolt stop. I've read on other posts that their bolt stop was sticking because of gunk around the bolt stop.