I had a discussion once, where the other person answer got deleted due to personal attacks (issue described here). Since then every few days about 2-3 of my questions/answers are downvoted at exactly the same moment. I must tell, that previously I usually had no more than 1 downvote per 4 months or more, so it turned my attention on.
I think the person got mad at me and will continue with his behaviour. He found a smart way to skip the validation as he never downvotes too much, so the algorithm won't detect him. As so, my points never returns.
I may be wrong of course, but it seems suspicious for me. How +- does the algorithm to detect serial downvoting work? Does it check the IP/user of the up/downvoter between days or just during 48hour period?
I'm not so popular to have high probability of 2 people at exactly the same moment downvoting my questions. As you may see, often it's the only activity on my profile.
Disclaimer: I don't claim the person is male, I refer the person as "he" for simplicity. It's not that I care so much about these virual digits, but it feels a bit unfair.