odd indeed...

I have used my cast iron for over a year - no problem. I don't understand how this could even happen.

I cracked one on an old fashioned electric coil last year. It could have happened on any cooking element, a.f.a.i.k.

I've cracked cast iron, too. Sounds like a rifle shot. I had just rinsed and oiled my dutch oven and put it on the burner to dry it. I ended up leaving it on too long and kah-chang!
It was my fault, of course. Iron is famous for holding heat, which is another way of saying it doesn't conduct heat all that well. It is also brittle. Putting an empty or relatively empty iron vessel on the burner is a recipe for getting it heated unevenly, causing uneven expansion, high stress within the metal and a loud crack when it all lets go.
Now I try give an iron pan more time to warm up, over no more than a medium flame, and I haven't had any more problems. It might be good to baby iron over an induction burner, too, for the same reasons. Once there is a good load of food on board, you can probably turn it up to high.

How big is the heating area of your hob? If there was a lot of unheated overhang and the heat was set fairly high, the temperature gradient could have been different enough to crack. That's something that could happen with any type of heat source, but with flame or pre-heated standard electric, you're more aware of how high the setting is because you can feel or see it, too.

I don't know how induction burners regulate their settings-whether they adjust the current output like a standard electric coil or whether they vary the frequency interval of the same current pulse-like a microwave. If it's the latter, it may be difficult to gradually warm an oversized pan. The induction experts or Lodge should have the answer to that one.

If the griddle doesn't have a flat bottom-if it's a little concave or has ridges, that would cause uneven heating which might cause cracking.

Please let us know what Lodge has to say.