Although I do not recall which update triggered the issue, I suspect it has something to do with the division of cannon controls to the gunner and rocket controls to the pilot, when previously the gunner was the only one with control of the rockets, triggering the opening and closing of the weapon pylons when toggling between cannon and rockets.
Now that the Pilot has permanent control of rockets without having to activate manual fire, the pylons remain in closed position despite having rockets being constantly selected by the pilot