So back in the 90s the printer driver in Solaris had a memory leak[1]. At the time I was a contractor for a big bank that is sadly/not sadly no longer with us any more. This was when the status of faxes in confirming contracts hadn't been sufficiently tested in court so banks used to book trades by fax and the system that sent the fax would also send a document to a particular printer which would print the trade confirm out and there was some poor sap whos job consisted of picking up the confirms from this printer, calling the counterparty and reading them out so that they were all on tape[2] and legally confirmed.
Anyhow one day the memory leak caused the printer driver to fall over and fail to print out one of the confirms so the person didn't read it out on the telephone. The market moved substantially and the counterparty DKd the trade[3]. A lot of huffing and puffing by senior executives at the bank had no effect and they booked a $5m loss and made a policy to never trade with that particular bank again[4]. The fax printer job was moved to windows NT.
[1] According to the excellent "Expert C programming" this was eventually fixed because Scott McNealy, then CEO of Sun Microsystems had been given a very underpowered workstation (as CEO) so was affected a lot by this problem and eventually made enough of a fuss the devs got around to fixing it https://progforperf.github.io/Expert_C_Programming.pdf
[2] Calls in the securities division of banks are pretty much always recorded for legal and compliance reasons
[3] DK stands for "Don't know". If the other side says they "don't know" a trade they are disputing the fact that a contract was made.
[4] Which I'm sure hurt us more than it hurt them as they could just trade somewhere else and pay some other bank their commission