> I have heard from users having as many as a thousand karma points that were shadowbanned without warning

I don't think that can be true, at least not in the last 12 years. Far more likely is that someone incorrectly concluded that they were shadowbanned. But if anyone wants us to check a specific username, we'd be happy to do so.

People come to all kinds of mistaken conclusions, especially when they're upset about something that we or someone else did on HN. Self-reports of this kind, especially about being banned, are mostly unreliable.