Along the way during my love affair with my M1 I have had similar problems. In almost all cases the problem has happened with light loads (when shooting clays) and has been solved by a tap on the bolt handle with the off hand to get the bolt moving forward.
Sqirting a little oil onthe relevant moving parts always seems to improve the situation.
I have figured that it is a combination of light loads and lack of cleaning. I can only remember one similar malfunction with heavy upland game #6s and even those don't generate the recoil of a decent tactical load. That was while hunting in a very dusty area near the end of the day, the gun was pretty filthy.