Anecdotally I've noticed bot-like behavior on HN down-voting posts almost immediately, before a human could have read them. This is followed, typically, by a correction over a few minutes and then regular up- (or down-) voting resumes. I can imagine that HN is subjected to quite a lot of novel attacks of this nature, and I don't think it's in anyone's interest that they broadcast the details of it. My advice: be patient and take downvotes with a big grain of salt. They may not mean what you think they mean.