When an app misbehaves or quits this is what I try to remedy the problem:
1. Quit the app and start it again. Double click the Home button to show the screen with running and recently used apps. Each app icon will have a sample page above it. Flick up on the page (not the app icon) and the page will fly away and the app icon will disappear. This quits that app.
2. Quit the app and reset the iOS device. Double click the Home button to show the screen with running and recently used apps. Each app icon will have a sample page above it. Flick up on the page (not the app icon) and the page will fly away and the app icon will disappear. This quits that app. Then press and hold both the Home button and the Sleep/Wake button continuously until the Apple logo appears. Then release the button and let the device restart. You will not lose data doing this. It's like a computer reboot.
3. Quit the app like I described previously. Then delete the app by tapping an holding on the app until it begins to jiggle. Tap the X and confirm the deletion. Then reset the iOS device. After the device restarts use the App Store app to download the app again. You will not have to pay for it.
4.c After trying the steps above, if the app still quits or doesn't work, contact the developer of the app to report the problem.