You can solve many game performance issues (i.e. loading, crashing, missing features, sync-ing of the game)  with the following ways:

1. Check your Internet connection
  • Make sure that your device is connected through WiFi, 3G, 4G, 5G, or LTE.
     
  • If you play through a WiFi connection, make sure your router is on. Additionally, try not to play too far away from it, as you may lose the WiFi signal.
     
2. Restart your device

3. Make sure you have the latest version of your game app installed from the iTunes App Store.
 
  1. Open your App Store.
  2. Tap on your Profile in the top-right corner.
  3. Scroll down to the Upcoming Updates / Available Updates section.
  4. Tap Update next to an individual app, or tap Update All.
4. Restart your app by force-closing it:
 
For devices that have a Home Button:
 
  1. Press your Home button twice quickly.
  2. All your open apps will be displayed. Swipe left or right to locate your app
  3. Swipe up the app's preview image.
  4. Return to the Home screen and restart the Game app.
 
For devices that don’t have a Home Button:
 
  1. From the Home screen, swipe up from the bottom of the screen and pause slightly in the middle of the screen.
  2. Swipe right or left to find the app that you want to close.
  3. Swipe up on the app's preview to close the app.
5. Force close unnecessary background apps using the same steps as above.

6. Make sure that you have the latest software version of your device's operating system.
 
To check if there is a system update available:
  1. Open your device's Settings app.
  2. Tap "General" > "Software Update".