If cocoa butter is melted at a temperature that is too high, it may burn and lose its smooth texture.
Your chocolate may get lumpy if the cocoa powder isn't sifted, which will reduce its smoothness and silkiness.
Chocolate that is not properly tempered may have a mushy texture and a dull look rather than a hard, glossy finish.
Too much sweetener can change the structure of the chocolate, making it excessively sticky and mushy.
Chocolate "bloom," in which fat or sugar rises to the surface and forms a yellowish covering, can result from not keeping chocolate in a cold, dry location.