Yesterday (and again today) it appears that someone was going through FATE questions for the first time, upvoting the ones that they thought were good, I suppose. But at the beginning of today, there was a negative value to equal the votes from yesterday with the description "Serial Upvoting Reversed". What does that mean and under what circumstances does that happen? I've seen this pattern before, i.e. someone new joins and upvotes questions under a certain tag- I've even done it before when I first started, and when I've been away for a while. Or I start playing a new game and going through the questions. But this is the first time I've seen this particular action.
This is an automatic attempt to reverse voting fraud, and it's not targeted on specific tags, but specific users. The algorithm says "If N% of User X's votes were for User Y's posts, that's suspicious" and reverses it out.
Unfortunately the algorithm does seem to catch upvoting in particular tags because certain people have many of the answers in those tags.