It is difficult to say what happens without the model. But i wonder if the rigid transform between the revolute joint and the spool can be the cause of the problem. If the sign or value of torque are adjusted, and you see no difference, it is likely it.
In one of our examples port R (spool) and port F (winch joint) are directly connected. https://se.mathworks.com/help/physmod/sm/ug/block-and-tackle-with-four-pulleys.html
Hope this helped out. BR Juan