For any issues with the iOS APP please try to reinstall the app from your mobile device:
Check the app for any updates
Remove the app from your device
Restart your device
Reinstall the app on your device
If you continue to experience trouble, install any available software updates. If these suggestions do not resolve the issues you encounter, please try accessing the app through a different network or WiFi connection to see if the same issues occur.
For more detailed information please visit the official iPhone support page or the official iPad support page