We use a couple cast-iron skillets on our glass-topped electric-coil stove (likely from the 90s?). One skillet has a bump on the bottom that I haven’t filed off

We use a couple cast-iron skillets on our glass-topped electric-coil stove (likely from the 90s?). One skillet has a bump on the bottom that I haven’t filed off yet. The glass surface seems fine, but if you’re renting it makes sense to be cautious.