I have a friend who ordered two packages of bees, with the same shipment as me, at the start of the season. My hives are going pretty good, except they are a bit light on stores due to drought. One hive is a voracious foraging machine. I check them once a week, and have started feeding them again. I keep a sharp eye on them to prevent robbing, which has been an issue lately, especially with my strong hive. All of my weak hives now have robber screens in place.
At any rate, my friend checked his bees about a week ago, and even though they were light on stores, he said they were still present and active. He went back again and checked a week later when he noticed a lack of bee activity. Both hives were totally empty, and ants had moved in eating what was left of the brood and honey. He is convinced they both absconded. I think they got robbed out.
It seems odd to me that two completely different hives would abscond at the same time, even though they are sited near each other. It seems far more likely they were robbed out by a stronger hive in the area (hopefully not mine).