The gun is "jamming" in my opinion because of the silencer, which reduces the blowback to cycle the gun. Notice in the video, the shooter has to manually cycle the gun after each shot and is not surprised to have to do so. After the second or third short, the round does not eject smoothly and recycle requires a second cycle, but the shooter is not flustered. This person knows what they are doing. They are also not concerned about leaving shell casings behind. So this shooter has reason to believe this gun and ammo will not be traced back to them (or doesn't care). This shooter knew what they were doing.