Citibank mistakenly sent $900M to a bunch of hedge funds. Many refused to return it. Citi lost the court case.
https://www.cnn.com/2021/02/16/business/citibank-revlon-laws...
https://www.cnn.com/2021/02/16/business/citibank-revlon-laws...
And flash loan contracts are a bright neon sign saying "arbitrage opportunity!"
And they're a gigantic bank, it's the original digital business, every banker knows a single arithmetic error is dangerous.
Just bankers being inept.