Wasn't aware of that HOn3 coupler, had to look it up, seems they are using a similar spring placement against the pivot like Sergent, only against the compression when pulling rather than overrun in the sergents. This is probably what's causing the bouncing. Stretching the coupler out when accelerating, then pushing it back when the pull has reduced. The Sergent on the other hand, compresses the spring on the overrun and would release on acceleration. Because the train's couplers are in extension when pulling, the movement in the Sergents, while there, is not noticeable. Maybe also the Sergent springs are stiffer in compression than the Kadee's, further reducing the amount of movement.