> Even more interestingly, there was negative karma. I don’t even know how this came to be.

Brand new account commenting with very low value but not worth flagging. For example "I read the article yesterday" or "Why is this article even on HN?". I've seen a couple that had negative karma on the first days. Often though it's simply spam and the account soon gets shadow-banned though I don't understand the process that does that. Example user: https://news.ycombinator.com/user?id=gabriella4151