HN has limits on replies for threads that are popular, in order to prevent what it thinks is a back-and-forth flame war.

It can be overzealous at times.

Yes, but it does that by flagging and hiding the thread, not closing comments.

Both, actually. Both individual comment threads and individual users who post “low quality comments” too quickly get rate limited.

	▲	GeoAtreides 4 days ago \| parent [-]
		> individual users who post “low quality comments” too quickly get rate limited. only if their karma is low, OP's karma is not low