Cake sinks in the middle when baking. Only happens when I make a Coca-Cola Cake
Without looking at the recipe, I can't know for sure, but I have a couple of ideas. First idea is to check your oven temperature. Oftentimes ovens will run hot or cold, and you might not know it for years. Get an oven thermometer and match the pre-heat temperature to the temperature on the thermometer. That will help your cakes bake more exactly.

Next idea. You may be putting too much leavening in the cake. Too much baking soda or baking powder could cause your cake to fall, and it also can impact the flavor.