I saw Qifeng from Mengcheng Food analyzed it. There are several possible reasons for the collapse: 1. The meringue is not really stiff. , 2. Stirring for too long will cause the meringue to defoam and the batter will not hold up because it has no support. The mixed batter is very voluminous and flows slowly, not watery. 3. Using an anti-stick baking mold resulted in the cake shrinking due to lack of grip. 4． If it expands very well in the oven, it shrinks as soon as it comes out of the oven because it is not baked through and the texture is not set. 5. If the egg yolk batter is mixed for too long, it will become glutenous.