I have had a few phone calls from beekeepers that told me all their bees absconded from their colonies. The bees were gone or had very few left and the hives were full of honey.
Hives that display this type of behavior, are bees that have very high levels of Varroa.
In fall, a beekeeper looks at their bees and they look great, three weeks later they look again and all of the bees are gone. This is not colony collapse, it is Varroa.
Treating for mites in August could have prevented this from happening.