I happened to notice, that yesterday I received 20 simultaneous downvotes across 10 of my questions, all in the same minute.
I am curious what could have caused this?
I've done some digging with the mod tools, and I'm ~110% sure that you were a victim of serial downvoting. I've taken action in reponse.
Now, I can't manually reverse the votes, but the system should invalidate them within 24 hours - probably less, given that's already been about 20 already, and the relevant automatic scripts run regularly. It's certainly enough to trigger an automatic reversal. We'll keep an eye on this; if you experience targeted downvoting again, let us know with a custom mod flag on one of your posts.