It sometimes happens that the game closes or is slow. There can be several reasons for it.
Please try the following steps, even if you have tried some of them already. In some cases it helps to make the device and the game perform better.
1 – Close all your apps running in the multitasking bar as described here: https://support.apple.com/HT201330
2 - Make sure you are not running out of free space:
Go to Settings of your device > General > About > Available
It's suggested you have at least 20% of free space on your device out of total for the game to perform smoothly. If your storage is almost full, it may cause issues.
3 – Restart your device:
- Press and hold the Sleep/Wake button until the red slider appears.
- Drag the slider to turn your device completely off.
- After the device turns off, press and hold the Sleep/Wake button again until you see the Apple logo.
4 – Open the game. Play the game for a while and see if it helped or made any improvement.
In case it didn't help, please send us the detailed description of the problem.