Most issues with freezing and crashing are due to memory issues with your device. Following these steps should help!
1) Close all applications running in the background of your device
2) If your device's storage is getting full, clear out some apps to free up space
4) Restart your device (turn it off and on again)
5) Launch the Game Application, ensuring that you are connected to a stable WiFi connection and no other apps are running in the background