One last test to see if it's the link. Repeat test 1 with the gun upside down. Does the smoothness of the slide operation go away? If turning it upside down does terminates the smooth function, the link has stretched and is not pulling barrel down quite early enough in the cycle timing. That would vindicate HiBC's observation.
Flipped the gun upside down, no recoil spring, no shell in the chamber. The slide comes back almost 1/8 inch then I can feel it catch on the barrel lugs. It's quite not as hard to overcome the resistance as it is right side up with the shell in the chamber, but there is a definite catch there. I can feel the interference of the lugs.
Just to validate for my own sanity, I tried the test on my Argentine Sistema. There's definitely a big difference. Plus the Sistema starts to unlock immediately upon moving the slide, where the Star has that 1/8 inch of play where the slide moves back before it even tries to pull on the barrel.
So does a barrel link require fitting, or should it be a drop in replacement?