After updating your Xperia™ device to Android™ 5.0/5.1 (Lollipop), Android 6.0 (Marshmallow) or Android 7.0 (Nougat), you may experience problems setting the screen lock to None or Swipe. This only happens if you set a pattern or a password lock before you update.
To fix this issue, you need to clear the credential storage.
To clear the credential storage
- From your Home screen, tap the Application screen icon.
- Find and tap Settings > Lock screen & security or Security > Clear credentials.