I just read an article that they couldn't implement app thinning in the iCloud that's currently 'stable' - this beta uses a different iCloud capable of app thinning. So the entire system is in Beta, probably changing quite a bit to get it ready for app thinning, some of the updates might be related to app thinning, or they may be reseting the icloud servers cache / db's as they get the new iCloud ready for the general population.