Cracking chocolate is one of the most common problems with homemade chocolate covered strawberries and it almost always comes down to tempering.
Tempering is the process of carefully heating and cooling chocolate to specific temperatures to create a stable crystal structure in the cocoa butter. Correctly tempered chocolate sets with a glossy finish and snaps cleanly. Incorrectly tempered chocolate sets dull, soft, or develops bloom a whitish, streaky surface and is more prone to cracking.
The other common cause of cracking is temperature shock. If the strawberry is very cold when it is dipped into warm chocolate, the rapid temperature difference causes the chocolate to contract and crack as it sets. Similarly, refrigerating freshly dipped strawberries too quickly can cause the coating to crack.
Moisture is also a factor. Strawberries that are not properly dried before dipping will repel the chocolate, causing it to pull away from the surface and crack or peel.
At La Fraise, we temper our Belgian chocolate correctly for every batch. This is one of the reasons our coating looks the way it does glossy, even, and stable. It is a step that requires time and attention, and it is why professionally made chocolate strawberries look and behave differently from a rushed homemade attempt.
If you are trying to make them at home: dry your strawberries thoroughly, bring them to room temperature before dipping, temper your chocolate properly, and allow them to set at room temperature before refrigerating.