I'm not "brushing mistakes off", at all. The process that led to the bugs needs a full review and root-cause corrective action, especially enhanced testing scenarios. I'm just pointing out that software "being wrong under load" is not some sort of crazy, unusual problem that points to poor software architecture. These bugs can easily be caused by a single line of code that wasn't synchronized correctly.

... ... that's the problem. why isn't it running isolated?

In most industries that are not IT, testing the IT systems very well is needed, but rarely achieved. In my area (FDA regulated) performance testing is almost never done correctly and (for sure) never completely, but as long as it works and the auditors never look at these details nobody from management is willing to know about it, because fixing it costs money. For many years the people signing off for all the software were intentionally not business people with zero IT knowledge, so they could not be accused of knowingly signing off low quality code. That saved tens or hundreds of millions of dollars in the past 20 years alone.

> In most industries, testing the IT systems very well is needed, but rarely achieved.

FTFY. IT shops on the whole aren’t any better here.