It happened to me many years ago when I baked my first meringue-based Angel cake. The cake split into a dense, moist bottom layer and a light, dry upper layer. However, this never happened with Japanese Cheesecake. I assumed that the meringue, folding technique, and oven temperature were the reasons behind it. To avoid any mishaps in these areas, please refer to the FAQs above and follow the instructions closely. Another possible cause of this issue may be your oven. If your oven's temperature is uneven or inaccurate, it could lead to this problem. If you're dealing with a meringue-based cake recipe for the first time, don't get discouraged if your cake turns out this way. Remember, practice makes perfect.