Just playing devil's advocate here:
That's not Brigade Capital's problem, and that's also not Revlon's problem.
I think it's entirely obvious brigade should return the money. But, playing devil's advocate:
Brigade gets a payment, 'out of nowhere' (it wasn't agreed upon beforehand, nor part of the repayment schedule), from the bank of Revlon, earmarked 'revlon'. Hey, the intent is clear enough, and Brigade sees this as an implicit contract. This transfer can be seen as equivalent to a note from the bank: "I, CitiBank, in my function as the bank of Revlon, hereby prepay some of the debt, and whilst revlon did not personally sign this note, that is okay because I am their bank, you can trust me."
And Revlon, having made no such agreement with citibank, also 'wins' their case and this money isn't scratched out of their accounts.
CitiBank, having made the error, is going to have to eat the 9 digit loss, but is of course allowed to recoup it, according to the normal schedule, and without charging interest (not that this matters much, what with interest being near nil), vs. revlon.
If revlon goes broke before they can, that's a bad day for citibank.
NB: To be clear I think when talking about 9 digits, this is a preposterous interpretation, but it IS one.