With the release of iOS 9, Apple is becoming more forceful with its push to get users from iCloud over to iCloud Drive. The old iCloud simply won't work on iOS 9 devices. We apologize for the inconvenience this may cause, but it's beyond our control.
If you want to continue to use iCloud for syncing, and don't want to upgrade from iCloud to iCloud Drive, you'll need to stay on iOS 8 or earlier. Otherwise, we suggest you upgrade to iCloud Drive.