I used iCloud backup for both my iPhone 6+ and iPad Mini 3 and the backup has been successful for months. I never synced both of my device to iTunes in my MackBook. Yesterday, I connected both of the devices, NOT synced it, but to do manual backup. The iTunes backup were successful. However, I noticed that iCloud backup is now DISABLED. The problem is, when I turned on iCloud backup again, the iCloud backup ALWAYS FAILED with message "The last backup could not be completed". Can anyone help me? Or iCloud backup is incompatible that once I did an iTunes backup, the only way to turn it on is to reset the devices?