It’s the recoil from the gun, a tank needs to have very good recoil control, if the tank didn’t move like that to cancel the forces from the gun and stayed stiff it would basically destroy itself from the vibrations of the gun. It’s a normal thing. Some extra movement may be seen due to the skirts over the tracks. It’s also firing over it’s side which means less of the length of the hull is receiving the recoil (in the opposite direction to the recoil). All these factors combined make it seem like it’s wobbling too much. But it’s nothing out of the ordinary.