He needed a Neilsen device or piston in the suppressor to assist with cycling on the action, which he didn't have.

He's not surprised that he has to rack the slide after every shot, he knows that it most likely will not cycle and he'll have to work it manually and he reaches immediately to do it.

edit: i'll speculate and say the suppressor still worked after the shooting because he still had it on him. if it was melted or broken, he may have been more apt to toss it.