I believe Hacker News does this too (disclaimer: I have never experienced this firsthand, and the people I hear it from are obviously not impartial sources).
I’ve experienced this. If you are downvoted in quick succession you will get a “you are posting too quickly” error if you try to reply to anything… even if you didn’t post anything except the original post. Seems to last about a day.
They did that to me years ago, like ten years or so. Took me weeks to figure out the site wasn't slow when logged out! They don't do it anymore (and thankfully, because if they did it to me now I'd slowloris the hell out of this site).
That's rate limiting. This is enabled on accounts if you ever post something "controversial". Shadow banning, where the site lets you think you are posting successfully, has definitely been used in the past on this site and probably still is.
