Probably some automated anti-spam algorithm they've put in place, but it seems pretty stupid, unless you're copy/pasting the SAME comment repeatedly across Medium.

I've been slapped (not here, but on other sites) for TYPING TOO FAST. Sorry, not sorry. I'm a touch typist. Is that such a thing of the past that it's now the hallmark of a spammer?

I'm sorry to hear you've been rate-limited by Medium. You sound like exactly the sort of commenter we all want, not the spammy kind.