The issue has affected a growing number of users on the Apple Support Communities, MacRumors discussion forum and social media.
Apple recommends restoring your device from an iTunes backup to resolve the problem.
1. Connect your iOS device to your computer and open iTunes.Apple released iOS 9 on Wednesday for iPhone 4s or later, iPad 2 or later and the fifth-generation iPod touch or later.
2. Select your device. If you don't see it listed, force restart your device by pressing and holding both the Sleep/Wake and Home button for at least 10 seconds, until you see the Apple logo.
3. If you made an iTunes backup of your device before updating to iOS 9, restore your device from that backup. If not, you need to make a backup of your device in iTunes, then restore from that backup.