The Game Studios are constantly working on improving our games by introducing new features, gameplay or concepts. They closely monitor a game's difficulty, listen to player feedback about levels or features and may tweak things to enhance the player experience. For know more about it, read here https://community.king.com/en/candy-crush-saga/discussion/249891/has-your-level-changed
https://youtu.be/7OvvfE8tGGU