First year keeper in Wisconsin, I had what looked like a healthy hive that just disappeared in October. Early October I took off the super and winterized it with a vented super+woodchips+mousegard. This week I took a look, and there were about 20 bees and the queen in the hive center, no other bees. The hive was a double brood box, top was completely full of capped honey, bottom was about 1/4 capped, 1/4 uncapped honey/pollen (the rest were clean open cells). There was no mite problem, and all the cells seemed in good order (no evidence of robbing, no deformed brood), and not many dead bees around on the ground. Is this just a case of bad luck, or am I missing something I should look for?