AR Failure to Feed - Please Read

[Hawk]

If I understand your issue correctly your AR will not strip the first round (on a full mag) completely off the mag when you manually drop the bolt. It feeds fine on the remaining rounds.
The rifle is new?
The mag's (all of them) are new? Same brand mag's?
You're loading them each time with 30 rounds?
Brass or Steel cased ammo?
What happens if you load just a few rounds in the mag and try dropping the bolt?

I suspect it's just the new mag's. Try loading the mag's 1-2 rounds shy of 30 rounds and see what happens.
It could also be excessive resistance on bolt travel. Sometimes the bolt assembly needs a break-in period before they run smoothly.

Let us know.