I agree that the headspace or firing pin is out of spec. Having recently gone through cheap stuff with nothing but frustration I stumbled across an addage that really hit home and applies to this situation as well. "Only a rich man can afford a cheap scope" replace scope with upper in your case. Cheap is OK if you have the tools knowledge and experience to and inspect yourself, and fix yourself if needed... otherwise you will waste money on return shipping and lose time... or worse get injured.
Only the rich can afford that crap.
Only the rich can afford that crap.