Does HN actually suffer this? I know its done on Reddit and by who in one case; just having a family member active in politics gets you good insight how many sites they try to manipulate.
I was hoping that HN's flag system would sufficient for the community to self censor. Perhaps we need a flag on comments too, something you can't see. I would also prefer that posts don't transition through the lighter grays as they get down voted but disappear completely once the dead threshold is met. That would prevent some piling on that does happen
Another possibility is that voting rings for _other_ posts flag maliciously to remove the competition and give their posts a relative boost. Maybe author can find correlations with other posts that were showing on the front page at the same time as the flagged ones and see how _their_ rankings got boosted due to the flagging.
I've chatted to mods on various sites over the years and I've heard that "voting rings", particularly the automated ones, often try to obscure their upvotes by also upvoting obscure stories and downvoting competing stories.
Likely if IP A posts a story and IP X,Y,Z always upvote it first, it likely flags that as suspicious. Or if IP X,Y,Z go directly to the link and upvote, instead of organically finding the post.
So some articles might simply disappear because the OP asked too many friends for upvotes or because of false positives.