iPad won't backup to iCloud; get "
My iPad is plugged in to an AC power source, connected to WiFi, left overnight, and no backup.
Went to iCloud > Backup > Back up Now, it said "Backing Up" for about ~5 minutes, and then I get "The last backup could not be completed." No explanation beyond that (see screenshot below).
Tried restarting the device, same thing happened. I tried looking at the various support articles, but none seem to offer any other solutions.
Any suggestions? Thanks!
iPad Air 2 WiFi, Cellular, iOS 8.3