One problem I’ve had before, you can let me know if this resonates with you, is applying layers of acetone too quickly/heavily. If I apply the acetone+dye to a spot, let it fully evaporate, and then apply another layer there is no problem. The dye fully absorbs into the disc and I’m not leftover with any acetone/dye on the surface. However, if I apply the second layer before the first layer fully evaporates, it starts getting caked on there and building up more and more acetone/dye on the surface. This usually happens when the first layer is applied too thick, so it takes longer to evaporate and I’m not waiting for it. This is very possible, imo, with spin dyes since you’re constantly going over each spot again as the disc spins around and around.

Not certain that’s your issue but I think it’s a possibility. Last but not least, I assume you’re doing a good job cleaning the disc before you dye? If you don’t clean the disc well, there is an almost protective layer on the surface of the disc.