mine used to do this before her shed. there would be individual chale sheds ALL OVER her cage. she also had some whrinkling on a few scales on her spine. but when it was happening, someone told me it could be scale rot. i'd keep an eye in it till it stops. keep their bedding extra clean.

when this was happening to my snake, it was when i would soak her alot. i got laid off work so i had plenty of time to sit at home with my animals. i think the chlorine in the water induces this. the more i would soak her, the worse the scales would fall off. it's good to soak, but be sure to use the drops that condition the water and get the chlorine out. and don't over soak, if your snake feels dehyrated it will get in it's water dish.