have you looked at the front of the bolt carrier, piston, for signs of wear? it might be getting hung up where the gas tube and gas block meet. I had this happen using another carrier in a different rifle. would get the same result not going fully into battery but the piston was hitting the edge of the gas block and not seating fully. changed back to original carrier and rifle operated fine again. otherwise look for wear spots. also difficult to tell based on the pics provided, what the issue could be. need internal pics for better advice. hopefully others chime in.