You might occasionally encounter an error message telling you that a Recipe for an Item has been changed, and requires a restart of the game.
This typically does not mean that a change to how the item is built has occurred; simply that a new server update has been released and that the game must be restarted in order to sync with that change and ensure that all of the data matches.
Similarly, you might see an error message from time to time indicating that a server event requires a restart of the game. This means that a change has been made that requires a restart of the game in order to work properly, and will generally only occur when a game-wide fix to certain potential issues are applied.
When these errors pop up, please close the app completely (including force-closing the backgrounded version), and restart it. If the error continues to occur after that, turn your device off and on again.