If you pause playing in the middle of a level to use other apps (like checking email or social media), your device might quietly force the game to close. This happens to save memory and battery life.
When the app is forced to close, returning to the game will cause it to restart. You'll lose any progress made within that level, and the life you used will also be gone.
The amount of time before a device does this varies and is outside of our control. Because of this, we recommend finishing any important actions in the game before switching to another app or letting your device go to sleep.