I'm not sure what i can do to replicate this as it seems random, but when you go from full nelson to wrestling stance sometimes i'd have the option to punch them in the face while being at the 7th grappling stage thing, when it's a option choking the enemy does nothing for my erection and nothing really happens until i ether penetrate or get off them.
I'll try to get a screenshot of the screen the next time that happens.