Clutch slip - What would cause this kind of wear? (2013 Daytona 675)

I took my clutch apart a few times to try to fix the slipping without buying new plates. I sanded the steel plates and replaced the springs. I measured all plates and they are all within manufacturer spec but the clutch slips anyway. So I open the clutch again and I see that this time one side of the middle friction plates is eaten up evenly on the internal diameter. All the other plates are as I left them. The side that was eaten was facing the engine. What could have caused this?

Also, I am thinking to buy new friction plates to fix the slip. Am I fine to reuse the steels as they are not warped, glaze has been sanded off and they are within spec width?