Could be variable results from variable ingredients. Apples are a natural product and include natural variation. Chances are the water percentage change from one fruit to the next would not be huge, but it could contribute. Size of the apples used, now, that could be interesting. I have three apples in my kitchen right now that could be termed medium sized. Respective weights: 184 , 188 and 237 grams. Now lets say Norm likes big apples and he uses 4 large apples (Why buy anything else?!?). But lets say I am cheap, so I took 4 apples from my bag of small apples from the discount bin. Suddenly Norm is adding 800 grams of apple to his cake, while I end up only adding 400.
This may not be what is going on. But to answer the question "Is something wrong with this recipe?", this is the first thing I think about.
