I THOUGHT that that might be the problem.
The helical slot is on the bottom of the barrel. The corresponding lug is on the locking block, which is assembled with the recoil spring assembly passing through it. The way the gun works is that, as the cartridge is fired, the slide and barrel (locked together) recoil together, for a short distance (roughly 1/8" - 1/4"). At that point, the helical track in the barrel and the lug on the locking block act together to cause the barrel to rotate 30 degrees, thus unlocking the barrel from the slide. Then, the slide continues to the rear, while the barrel stays put.
On your particular pistol, there is apparently a machining error on either the track in the barrel, or the locking block. Thus, the barrel is not fully rotated (30 degrees) as it should....but it is rotated enough to unlock from the slide (otherwise the gun would not function). There is a slot in the slide, through which the tab (locking lug) on the barrel rides as the slide recoils. Since the barrel is not rotating as much as it should, the locking tab on the barrel is being struck by the slide as it recoils, thus "beating up" the locking tab. However, the force of the impact is evidently then causing the barrel to rotate the rest of the way, so that it then slips into the groove in the slide. So then the slide continues it's movement to the rear.
In any case, I would assume that Stoeger will replace the barrel, the locking block....and perhaps the slide.
This problem is interesting and it is indicative of the issues possible with the design of the Cougar. The Cougar is a relatively expensive and complicated pistol to manufacture, due to the precise machining necessary to get it to work properly. As you can see, if the machining is not spot-on, then problems will occur.
If the parts ARE correct, however, then the gun functions beautifully. At least, MINE does.....and has never malfunctioned in any way.
I'm glad that Stoeger has gotten to the bottom of the problem. As I said, I thought that the problem might lie with barrel timing. I'm sure that they will make it right for you.