iCloud Drive remains in beta, even alpha, status
I wished to use an iOS device while traveling, so I copied 60+ GByte of data from my portable computer to iCloud Drive.
Fundamentally, it doesn't work even after waiting many days for all the data to synchronize. On iOS devices (iPad and iPhone) I have observed "Encrypted Files" and "Encrypted Folders" in the iCloud area of Settings (Manage Storage) and these encrypted files/folders typically do not appear in the folder menu when attempting to open an iWork document via iOS. The folders/files all appear on iCloud.com (viewed with a web browser).
I have worked, many times and over 2 weeks, with an Apple Senior Advisor, who in turn has contacted Apple Engineers. Despite trying many things, so far, no one has a solution or even an understanding of why the problems have occurred.
I cannot recommend iCloud Drive for any serious usage until Apple solves the balkiness of iCloud.