I just completed my first three gun match today and had an issue with my safety on my ar. After one or two double taps my trigger would you feel as though the safety was on.  I was confused as to why my gun would not fire as the safety selector was still pointing to the fire mode.  Cycling was not the problem as the gun successfully ejected and loaded a new round. After flipping the safety to safe then back to fire the gun would fire as normal. Has anyone had this problem before or have any idea what the problem might be?

Weak spring or is the stock nut loosening up and causing weak spring tension.

Thanks for the information. I took everything apart today and checked for burs and lubed everything.  I have another match this weekend hopefully everything goes well.