I've not run into a problem like this but what I would do is inspect the gas cylinder & front sight to see they are OK; If I had another, I'd swap & try again to zero the rifle. I'd also inspect the stock ferrule & lower band to see if they are OK & not damaged. I'd check the trigger guard & make sure it is locks in properly & pulls the receiver into the stock properly. Finally, I'd inspect the rear sight & make sure each part is OK & fits together properly.