First you should check if the flakes are skin or dried minoxidil. Skin won't dissolve in alcohol/ minoxidil. Putting a flake into a drop of minoxidil should answer the question.
If it is minoxidil, it means that the minoxidil is not being absorbed properly.
1. The minoxidil solution is drying too fast.
Try to add Propylene glycoleum and make sure not to blow dry or be in the sun for some time.
2. There skin is too dry to allow absorption. Dry skin means too little fat which hinders alcohol absorption.
Try to add 10% water to the minoxidil solution.
Or try to apply coconut oil from time to time to your scalp and/or use less shampoo.
3. Dermaroll for absorption with 0,5 -1mm roller. Roll every day with little pressure and only scratch the surface. 1mm is only for long hair.
For me personally all of the things did the trick with ru. Gonna add minoxidil once it arrives.