Colors not sticking after new MSC coat

[r_starlord]

Hey so I'm kind of new to the repainting stuff. I've been trying to work on two practice dolls right now that I'm having a lot of trouble with. After I use acetone and clean the face, I give the head 3 sprays of MSC and let it dry 30 mins between layers. Once I start working after the 3 primer layers everything is fine, the colors are sticking and everything until my pencil starts sliding and I add on another coat of MSC. Well, every time I go back in trying to work on the doll after this additional layer, it ALWAYS starts scratching away at the work I've already done and at the new MSC layer making it a total mess. It's driving me insane and I have no idea how to fix this issue lol can somebody help me what I'm doing wrong or give me some fixes to it. Thanks!