The behavior you described is due to a phenomenon known as "condensation" or "sweating" that occurs when cold chocolate is removed from the refrigerator and exposed to warmer room temperature.
When you place chocolate in the refrigerator, it gets chilled as the temperature drops. However, when you take the chilled chocolate out of the fridge and expose it to a warmer room temperature, moisture from the air can condense on its surface. This happens because the air in the room contains some level of humidity, and when it comes into contact with the cold surface of the chocolate, the air's moisture turns into water droplets on the chocolate's surface.
These water droplets can then dissolve some of the sugar in the chocolate, creating a thin layer of moisture on the surface. As the moisture dissolves the sugar, it forms a syrup-like consistency, which can make the chocolate sticky or even appear to be "melting."
On the other hand, if you store the chocolate at room temperature (without refrigeration), it remains at a stable temperature, and there is no drastic change in temperature to cause condensation when taken out. Therefore, it doesn't exhibit the same behavior of melting or becoming sticky like it does when taken from the refrigerator.
To avoid condensation on chocolate stored in the refrigerator, you can take some precautions:
Allow the chocolate to come to room temperature gradually: When you take the chocolate out of the fridge, let it sit at room temperature in its sealed container for some time before opening it. This helps reduce the temperature difference between the chocolate and the surrounding air, minimizing condensation.
Avoid frequent temperature changes: Try to avoid placing the chocolate back and forth between the refrigerator and room temperature, as frequent changes in temperature can lead to more condensation.
Proper packaging: Ensure the chocolate is well-sealed in an airtight container or resealable bag to minimize exposure to air and moisture.
By following these tips, you can help maintain the quality and appearance of your chocolate, whether you choose to store it in the refrigerator or at room temperature.