iCloud Drive no longer syncing between devices.
Between home and work, I regularly work on 2 iMacs (each running OSX 10.10.5), an iPad and an iPhone 6 (each running iOS 8.4.1). Only recently have I set up and started using iCloud Drive, i.e. about three weeks ago I uploaded several folders containing many documents, and everything was accessible and remained in sync on all my devices.
Starting a few days ago, I notice that documents created and saved to iCloud on one device no longer appear on the others. Pages documents cannot be found in either the dedicated Pages folder on the iCloud Drive or in the folder to which I saved them. Documents created in other apps (MS Word, etc.) do not sync either.
Does anyone have an idea why iCloud would working perfectly for a couple of weeks then suddenly stopped syncing?