I recently performed a paint correction on the roof and trunk lid of a classic Prius using Hyper Compound and a pair of Optimum MF cutting pads. The pads were cleaned and rotated after completing each section. After the final cleaning up, I noticed that both of them are exhibiting signs of severe compression or failure of the center 3" of the foam core, so that they are now visibly concave.
The pads were brand new and installed on my GG6 DA; they were never run with the machine over 5. I cleaned them between sections using Mike Phillip's terry towel technique followed by the nylon pad cleaning brush, both with the machine set at 2. At the end of the job, I washed them under running water after spraying with Pinnacle XMT pad cleaner, then let them air dry on a Grit Guard.
Any idea what might have happened to them? My suspicion is that this is related to the cleaning process between sections, but I don't think I did anything improper or unusual.