First let's acknowledge that this could very easily be a misconfiguration issue.

But, I'd be a lot more inclined to that idea if it wasn't for how they failed: they started a defrost cycle that turned the freezers into heaters, spoiling the food quicker. And the failure happened overnight, delaying discovery of the problem.

It could be just a compounding of bad luck. But an attacker with access to the specs for the freezers might be aware of how long they would stay cold after being simply shut off.

I was thinking timezone update - because of course an internet-connected freezer needs updated zone info so one can configure defrost schedules without the benefit of UTC.