And why didn't you made a Backup before the update?
Most Android apps perform auto-update.
Google Play Help - Update downloaded appsYou can update your Android device's apps individually or allow them to be updated automatically. Keeping apps updated gives you access to the latest features and improves app security and stability. Note: If Google determines an app update will fix a critical security vulnerability, we may make certain app updates regardless of update settings in the app or on your device.
Pretty sure the Jax wallet doesn't auto update the keyfiles. Something is fishy here.