If the bolt catch works when you manually cycle it on an empty mag then another possible cause could be short stroking. Are NEA gas blocks pinned or clamped? Maybe the block is slightly misaligned or the gas port in the barrel is undersized?
Take one of the uppers from your other AR and run it in the NEA lower, remove the ambi bolt release and see if the problem continues.
Take one of the uppers from your other AR and run it in the NEA lower, remove the ambi bolt release and see if the problem continues.


















































