Money disappearing from a bank account is a "comparatively minor failure"? Sorry, I stopped reading at that point.
But compared to, say, tens of thousands of investment transactions for pension and retirement funds evaporating, disbursements to a hospital's operations budget being delayed, sending confidential historical balance records in bulk to a large corporate customer's competitor, having an online investment system down during a period of extreme market volatility, or even large-scale customer data breaches, then yes. 'Money missing from a bank account' is in every significant way a comparatively minor problem probably fixable with a phone call and a couple hours of investigation on the bank's part, even with a significant sum of money. The bank would almost certainly catch it themselves during an automated audit. It's exactly the sort of problem that bookkeeping organizations are designed to mitigate and root out if they do happen.
The others could affect many, many more people's lives for much longer— potentially permanently.
- took a trip to the neighboring country, my friend tried to take out money from an ATM; first two transactions failed, third succeeded (at the atm). In the bank though, all "succeeded", and money were gone (first 2 eventually were reversed with manual intervention).
- I sold a house (in a remote mountain village), buyer sent 8100EUR from Germany, 78xy.z EUR made it to my personal bank account. Apparently due to multiple currency exchanges, but this is a SEPA transfer between two accounts both denominated in EUR, this was absolutely not supposed to happen and nobody was able to articulate exactly "why it happened" (or even exactly what happened). For this one the buyer decided to just eat the loss and sent me an additional 300EUR.