The other possibility is the little control arm, also called the "Fleming". It pushes on the rope from the outside, causing the rope next to the gypsy to engage the gypsy's teeth and move inward or outward.
The spring providing the pressure on the Fleming can break or weaken, letting the rope slip instead. Pushing on the Fleming with your shoe (no bare toes or fingers, please!), will then cause the windlass to operate normally as the correct pressure is supplied.
The obvious solution is to disassemble the windlass as necessary and renew the spring. If the Fleming is plastic (nylon) instead of metal and well worn, it should be replaced as well.
If you have the Installation Guide, which has also a parts catalogue, and feel mechanically competent to take it apart, dig in! If not, a local marine dealer should be able to do it for you. Lewmar (was Simpson-Lawrence until a few years ago), has very helpful on line techs that can help you with parts and technical issues.
Hope this helps!
Joe. :teeth :thup