Since you stated there was not much brooding, I guess that leaves robbing and high calorie activity.
You might want to look at the combs in the light hives for evidence of robbing vs regular food consumption. Are the cells ripped up as with robbing, or are they still intact?
If not robbing and not brooding, then that leaves food being consumed for high calorie activity. Flying is obviously a high calorie activity. If you have a lot of bees flying and finding no nectar sources, they’ll have to re-fuel their tanks from the stores inside the hive.