Prolly an issue with the gas system not letting enough gas through to fully cycle the bolt or a too heavy recoil spring or buffer or combination of those.
If it doesnt lock the bolt back with an empty mag your not getting enough energy to get the bolt rearward. Doesnt sound like a magazine issue
Saw this happen once when someone crammed a rifle length spring into a carbine buffer tube.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent