If you are experiencing a crash, performance, other hardware issue you might want to try this guide. There are some basic things you can try to get your game back on track.
For connection issues, please see this article here.
Force close the game
Especially if you're on a mobile device, try force closing or closing and reopening the game. This seems basic but it's sometimes all you need to do. For more information on force closing applications:
Close other apps
After the game has been closed, try playing for awhile without other applications open to see if this reduces the severity of the issue.
Turn your device off and on
Sometimes all your device needs is a fresh start. This is especially true if you are on a mobile device which is typically less powerful and can easily have a RAM build up.
Refresh RAM and clear cache
On an iPhone you can reset your RAM by holding down the power button until the 'Slide to power off' button appears, then hold down the home button for five seconds. The phone should return to the home screen, refreshing the RAM if done correctly. You can also clear cookies and cache from your browser.
Depending on your Android device, you can open Settings > Storage > Internal Storage > Cached Data. Tap this and confirm to clear the cache. You can also try opening Settings > Apps > Gems of War, selecting the app and the tapping 'Force Stop'. Some Android devices also offer a 'Smart cleaning' option which you can use to remove temporary files and caches.
Reinstall the game
Ensure your account is linked and you've noted down your password before reinstalling. Most devices allow you to press on the app and hold it down until an "X" or "Uninstall" option appears. On Android open Settings > Apps and navigate to Gems of War.; select the application then tap 'Uninstall'.
Note: Android does not always completely uninstall applications for up to 24 hours. If the app says 'Disabled' in the list of apps, ensure you select it then tap Uninstall.
Clear storage space on your device
Applications will become sluggish if you have less than 2 GB free on your device. Some devices come with 'Smart cleaning', otherwise you may need to manually uninstall applications, music, and photos that you do not want. Ensure you have backed up media you want to keep.