Welcome to the Forum rb -
Kind of difficult to diagnose from what you have written, but I will give it a try.
What kind of mags were you using? And what is the condition of the feed ramps in questions?
You said after about 12 rounds you started to experience problems, now, I can't see your weapon, but from the on line pictures, it would appear that the unit you have has an extremely short gas block on it, so more powder and "gunk" is getting back into the chamber because it is bleeding off closer to the point of ignition.
If this is the case, I would suspect that some oiling of the BCG and internals of the upper receiver in question would do you wonders towards getting it running correctly.
The AR basically operates by taking hot, gunpowder and residue gas and bleeding some of that gas back into the chamber to unlock the lugs and recoil the weapon, then the buffer and buffer spring, in the stock, compress and return the bolt and carrier to battery, picking a new round out of the magazine along the way.
if you have a bad, cheap mag that doesn't have the green follower and isn't lifting the round high enough, it MIGHT not be in line to be pushed by the BCG upon return to battery.
If your buffer spring isn't strong enough, and your feed ramp is a disaster of rough edges and dirty, the combination MIGHT be enough to cause the weapon not to be able to return to battery.
It's just too hard to give you a one answer fits all based on what you have told us.
Can you give us a little more info?
And, for what it is worth, I like the DPMS stuff. They are a little over-priced because of who they are, but they turn out a good product and usually stand behind it. That said, everyone turns out a lemon some time and it needs to be sent back, or touched up, to make it run right...
JD