This may be more likely to happen on a tablet rather than a laptop or PC. It is a device problem. The best thing to do is to turn off and turn on your device or shut the game down completely and start it again. To make sure the game has been completely shut down, it will have to reload from the beginning again and not just open at where you left off. You may search google on how to shut the game down completely on your specific device.
We also advise that these games should only be played using a web browser such as Chrome, Fire Fox or Microsoft Edge. These games are not designed to be played using the Safari browsers. It is also advised you have the latest version of the Chrome, Fire Fox or Microsoft Edge web browsers.