In level 4603 (and the crystal levels around that level), there is a bug.
If you match a candy UNDER a crystal candy, it breaks the crystal. You can only move a candy that's NOT ALREADY UNDER CYRSTAL to make the match. All well and good. However, the auto-hint function in the game suggests matching candy by moving a crystal that's already under crystal (see the screenshot below where the game suggest moving the green timebomb candy up to make a match - though because it's under crystal it's "locked"). This means if the only move you can make on a level is one of the invalid in-game suggestions, then the only way forward is to quit the level (losing any bonuses) and starting again because it won't reshuffle the candies.