Shouldn't the food be in the upper box not the lower box? Why did you (they) have 20kg of food in the lower box? Is it something you did previously that changed their normal habits?
I have nursed bees 48 years. Many things have happened. When I have 2 box hive, I put brood frames down before feeding. Bees fill the low box first because they brood are there. They they fill the upper box.
Frames must be full, otherwise bees do not cap the food.
When I say that I feed sugar on average 20 kg per hive, some have less and some more.
Bees have honey too in hives before feeding.
If I say something, it is mostly regular, because hives are quite individual what they do. It is not common that cluster eates first food from upper box.
My aim is not over winter 100% alive. It is imposible. If some die and I do not cry for them.
20% losses during winter and spring are normal to me.
So I have 20% spare hives as insuarance.