I've gotten sufficient evidence from support that voiceofra has been doing retributive downvoting. I've banned them without prior notice because I'm not giving them more chances to downvote.
I'm thinking of something like not letting anyone give more than 5 downvotes/week for content which is more than a month old. The numbers and the time period are tentative-- this isn't my ideal rule. This is probably technically possible. However, my impression is that highly specific rules like that are an invitation to gaming the rules.
I would rather just make spiteful down-voting impossible (or maybe make it expensive) rather than trying to find out who's doing it. Admittedly, putting up barriers to downvoting for past comments doesn't solve the problem of people who down-vote everything, but at least people who downvote current material are easier to notice.
Any thoughts about technical solutions to excessive down-voting of past material?
I think it's bad form to make costly (in terms of time) requests to moderators unless you're willing to be part of the solution. In this case, it would be good at minimum to outline exactly what you mean by a "transparency report" --- concretely, what sort of information would you like to see, and why would it be helpful? It would be even better if you were willing to volunteer to help in creating the report to the extent that the help can be utilized.