Induction range hotspot?
Here's 2 videos showing water boiling, you can see the hot spot is more pronounce with cast iron, I know it's not as good as a conductor but both pans are induction compatible.
I also tried the smallest pan I had and it seems better maybe because the coil underneath is not big enough. I also tried moving these bigger pans to different burners and had the same results as this is the biggest burner on the stovetop.
Cast iron pan:
Stainless Steel Pan: