I had my first freeze today. It happened while browsing the factory samples in the internal memory of my MPC One (Browse>Content>Drums). I was hitting the play button on the touch screen to preview kits, at one point this caused the MPC to freeze. Some parts of it seemed to still be working: the Play and Rec LED lit up when I pressed the buttons but I hadn't recorded anything or even assigned samples, so I couldn't tell if it was actually playing or not. Eventually I had to unplug it. On power up I got a warning that of course the MPC hadn't shut down properly. I cycled the power once more just to be sure, and everything was back to normal.
PS - I tried holding down the power button before unplugging it, but I probably didn't hold it for the full five seconds like it says in the manual. Which I consulted after the fact. Oops