Try the following.
- Close all iOS apps that are running in the background.
- Turn off the iPad, and then restart it.
- Delete the app and reinstall it ... ※
※ Use caution, since this will erase all data and settings.
Instruction of Backup data.
- Set your iCloud account on your iPhone / iPad.
- Tap the Settings icon in the upper right of the screen, and tap “Backup/Restore” > “Open”.
- Tap “Create Backup” in the upper right of the displayed screen.