As someone who thrives on tracking down rare but annoying bugs in a debugger, I love stories like this. It is not just bugs that cause real failures which can be headaches; but also bugs that just slow things down unexpectantly. They can sometimes go undetected for decades like this one.
I wrote an article this past year that talks about silent bugs that slowly eat resources and collectively can be very expensive in terms of wasted time and energy: https://didgets.substack.com/p/finding-and-fixing-a-billion-...