I’m in the wrong part of the world. Eastern Canada, exporting bees is too much trouble. Couple of things on over wintering. Is the hive being checked to see why they died? Big 3 where I am, maritime influenced 5A, are mite load, not enough food, and not enough bees.
Discussion
I think this last time he said moisture got in and maybe cold with it? There is drought here, so I wouldn't be surprised if a lack of food was an issue too.
Moisture in the hive with cold is a killer for bees. When looking at a dead out, if there are a bunch of bees with their butts in the air and their heads in the comb, strong sign of starvation.