This is likely due to your Internet connection dropping while playing the game. Not to worry though as it can be resolved as follows:
- Check that your device has a fast and stable internet connection here. The minimum recommended download speed is 3 Mbps, upload speed is 1 Mbps and a ping rate must be under 150 ms.
- If you're using mobile internet, try switching to Wi-Fi.
- Turn your device off and on.
If you are connected to Facebook in the game, clearing cache in Safari should fix it:
- Open Settings
- Scroll down and tap on Safari
- Scroll down again and tap on "Clear History and Website Data"
- Tap on "Clear History and Data" again
- Force close and reload the game before reconnecting to Facebook in the game