Our Boxer used to get it when she was younger had it tested at vets in case round worm or mites but all clear. Vet said it is common in Boxers and Dobi's, so as Staffs are related to Boxers (Bulldog genes) maybe it is the same, other appear to think so.
It would appear about now when her coat changed, two bald areas on her flanks, by full summer she was all back to normal.