Ok, so we have to include the Shin Jinseo misclick, right? It’s not too spectacular, since we don’t see the screen immediately, but the reaction says enough:
Ke Jie has a better reaction, though:
Actually the video on BadukTV shows Shin Jinseo’s screen that they do analysis over. You can see his mouse cursor (the hand) and where it’s pointing to place a stone (the coloured square). You can also see that the mouse cable is sitting on the laptops trackpad. I was watching back Yoonyoung Kim’s stream and she looked at a couple of different streams of the game
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To call it a misclick seems to imply that he actually clicked with his finger, which we can see he didn’t… I think accidental move is a better term.
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Does this one count? It’s not in a professional setting, but since the mistake only takes 5 moves to read out, I think it should… 
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As conversation is touching on this topic in Rudeness about the undo button, I guess it’s a good time to supply a bump.
https://senseis.xmp.net/?LadderExercise2
https://senseis.xmp.net/?IfYouDontKnowLaddersDontPlayGo
“Despite this blunder, O Meien went on to win the title match by 4-2.”
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Ladders happen. But is it really easy to prevent them?
I wouldn’t call something blunder just because someone didn’t resign more early.
What we see is continuation of not the best plan.
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Yes, ladders are and probably will forever stay a mystery to mankind. Prophecy says someday, the chosen one will come along and they will be able to track stones to the edge of the board. Til then, one side will have to resign when the other offers a ladder variation.
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Sadly the board position wasn’t recorded, according to the third tweet. 
I would’ve liked to see the board without the last move, see if we could spot it.
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It’s there, look at the english thread I linked.
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Why is 仲邑菫 translated to Nakamura Kaoru? Is that not Nakamura Sumire?
What was the penultimate move (that set up the position before Okada passed)? Perhaps a harmless looking dame fill adjacent to the key stones?
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I’m not sure if it’s a rookie mistake, I would’ve passed as well…
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It’s in a reply to one of the tweets in the original thread:
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Very interesting!
I found the key area and thought I’d read it out, but I missed White’s follow-up (3).
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Another unfortunate incident. Things are going crazy. I also find this one confusing. The main point is that someone moved a stone, there was a complaint after the game, and the result was overturned.
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Otake Hideo apparently overlooked a ladder, then resigned when his opponent played it 
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All crazy plays. A lot of good highlights as well,
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Here is a 15sec/move blitz game from fox between a Japanese 3p (as white) and a Chinese 2p… Apparently the Japanese 3p doesn’t know about the Flying Knife Ladder. Falling for what can be called “a classic middan bamboozle” (in topright between moves 35-45), he fell 15 points behind in fuseki by playing the infamous 3-3 joseki without having the ladder and never caught up.
Perhaps not a “rookie” mistake per se but certainly something one wouldn’t expect to see.
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