Recently I experienced issues with iWorks apps (Keynote, Numbers and Pages) synchronising across iOS devices and Macs. Even moving files out of iCloud Drive and re-uploading only one file, the issue persisted.
There is a solution to resolving this, however it may be possible that data will be lost if the following is carried out on older versions. The issue appears to be related to a synching failure with the files, to resolve this I opened each file and made a little change. Once completed I reactivated iCloud Drive across my iOS devices and all synchronised the files quickly.
The exact cause of this issue is unknown at the moment and I will continue to monitor to see if it occurs again.