Chocolate for baking should not be frozen or refrigerated if it is going to be melted. If you must do it, bring it to room temperature before melting and heat it slowly. It still may become grainy.
Chocolate chips that are frozen or refrigerated and are melted will get a "sugar bloom" and turn grainy.
Freezing candies or chocolate chips that will not be melted may only get a "bloom" a grayish cast that is fine to eat.
PB from MN