Margaret,
The bobbin tire could be hard and slick and or have a flat spot. It might also have shrunk a bit. The Simanco marked parts are quite old and the rubber can become hard and deteriorate when they get old. At that point they tend to slip and slid on the hand wheel.
Get some alcohol, I use denatured, and clean the tire and hand wheel to get all the oils off the surface. Then use a magnifying glass to verify there's no flat spots on the tire.
Personally I'd put a new tire on it anyway.
Several of my machines have the bobbin winding tire contacting the hand wheel at the same point as yours. I suspect the tire.
If your talking about the little pit in the bore of the hand wheel that's a non issue. I blew up and lightened your pic to see it better and I can't seen anything wrong with the hand wheel.
Joe