I understand what serial voting is in general, having read some of "What is serial voting...", but I woke up this morning to find the message -12 Serial voting was reversed in my 'reputation' achievement, and I don't understand what I've done. I'd like to understand so that I can avoid making the same mistake in the future.
The story so far: on a particular Stack Exchange site, a few months ago, I managed to irk a particular user. He then started going through my old questions and answers systematically and downvoting them. On a specific day, he downvoted 3 in a row, and so I searched Meta, where I discovered that "revenge downvoting" is a known problem.
I flagged those three answers, and the Stack Exchange site's moderators addressed the problem, to my mind successfully. They also said they had informed the administrators, but they didn't know if I would get my reputation back.
A week passed with no visible change, until this morning, to my surprise, the above message arrived. So I asked on that Stack Exchange site's meta site, where the moderators speculated that it might be a side effect of them having reported the downvoting. Perhaps administrators had discovered someone serial upvoting my posts and decided to reverse it.
However, this leaves me wondering if that's the actual case, or if, instead, the message was unrelated to the revenge downvoting and I had done something I should avoid doing in the future.
Also, what combination of vote reversals ends up in a 12 point change?