Starting with iOS 8, Documents are now synced via “iCloud Drive”. This is not compatible with the previous “iCloud sync”. Please see here:
It’s about iWork but the same applies for all other apps that use iCloud Documents to sync.
iCloud sync with iOS 8 will only work with OS X Yosemite, on which you have to switch to iCloud Drive as well.
By the way, you should have gotten a message regarding this when you chose to switch to iCloud Drive.