Indeed. I've seen it happen before and it appears that they have automatic downvoting based on some criteria, possibly just some classifier. I've attributed it to some bot attack before, but it's a bit too common now.
replyWhy does it being common downplay the bot attack to you? As time goes on, I'd assume bots activity to increase. I do not see it ever going away.
replybots get caught and downvoting requires reputation.
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