A Candy Shuffle is when all the candies on the board are shuffled. The colours of the candies don't change, but their position on the board does. A shuffle can be brought on when a player runs out of possible switches on the board.
When a player runs out of possible moves, all the candies go into a "Shuffling" word in the center of the screen and then they come out of the shuffled randomly.
After a shuffle, there would be a possible move, unless there are not enough candies to form a single one, in which case the player will fail the level.