I have been using HN daily since I was a teenager. I've seen that message maybe 10 times outside of serious issues in last 15 years. It's strange to me that it happens so frequently for you.
There's a manual rate limit that can be assigned to your account if you post frequently on controversial topics. Afaik once it's there it stays until removed by a moderator.
I've been seeing this multiple times a week for the past couple of years. It's gotten worse since 2020. I think that they are preparing to upgrade it, or did upgrade it?