Well, some data would be advisable. Is it a loss leader? Is their ice cream priced lower than wendy's, burger king, in-n-out or similar? To the best of my knowledge, none of those places have this problem.
If the cone is profitable to sell, then it's not a loss leader and they have every incentive to sell as many of them as they can.
Two of those three are not really marginal costs. Yes, it costs electricity to make the food, but _stable_ electricity is something you already need in the biz, same as rent. If you need a generator, you already have one.
Also, enlighten me: are markets where electricity grids are unstable the same ones where retail space is expensive?
I know this is hyperbole, just wanted to add a detail. This is a US-only issue. I don't think I have ever found a broken McFlurry machine in my part of Europe - and I had a LOT of McFlurries in my teenage years. I don't think they use the same Taylor machine here.
The dessert is part of what you are buying. You might as well say the cheese in a burger is a loss leader…
I can get soft serve from QT for .49 cents. I don’t think McDonald’s is intentionally losing money on ice cream to get you to buy Big Macs.