It has happened to me and I'm not coordinating with anyone. I have also experienced very rapidly upvoted submissions flagged, then I notified HN admins, had the post unflagged, but after that time it was deep past page 12 and got like 5 more votes over 24 hours.

I haven't seen the negative votes on submissions that people are reporting within this submission, but anyone who thinks HN isn't a target for myriad bad actors employing every means available to them to manipulate votes in whatever direction is a fool.