Recently, there was a global recalculation of reputation across StackExchange. People lost reputation points if one of their upvoted posts was subsequently deleted. Another reason that has affected a few people is that rapid runs of upvotes by the same user are reversed. The rationale for this second adjustment is that such runs of votes are tantamount to "block voting" or "voter fraud".
This has affected one of our highest-rep users and moderator, Mr.Wizard. He lost 420 points, and it is pretty obvious that there is a string of serial upvotes the previous day, so that is probably what the system picked up.
Just now, there has been another string of single upvotes on older questions, presumably to "compensate" for the earlier loss of points.
Mr.Wizard posts a lot of really good answers and yes, they are deserving of upvoting. But please, restrain yourselves. A couple of votes from an individual user to an indvidual user per day is plenty. Maybe leave ten minutes between them. Don't turn your accolade into an unwitting accusation directed at the target of your upvotes.
Whoever is serial upvoting him (or any other user) just to give them rep, please stop or at least slow down. It won't help them in the end.