Ive noticed that diffrent flywheel nutz have that groove that the spring sits in spaced from the flywheel diffrent. In other words, a mugen clutch nut has the groove closer to the flywheel than a sportwerks nut. When I ran mugen clutch and springs on my sportwerks flywheel and nut, shoes would walk off also. At first I bent the springs to pull shoes closer to flywheel. Eventually I got the mugen nut and all was well.
Maybe you have a simular issue. Hope this helps.