That happens to me as well. The same reason: not downvoting others while I never bought votes or used bid-bots, but still getting downvotes on almost all my posts. The worst part was when I was downvoted with a big % which also cut a big part of my payout ..but then I thought about asking nicely for a reason, but never got a reply, just another 5 accounts of the same person who downvoted my post again. and again, and again..