It's shocking to me too, but not very surprising. It's probably a combination of factors that could cause a failure of planning and I've seen it play out the same way at lots of companies.

I bet the original engineers planned for, and designed the system to be resilient to this cold start situation. But over time those engineers left, and new people took over -- those who didn't fully understand and appreciate the complexity, and probably didn't care that much about all the edge cases. Then, pushed by management to pursue goals that are antithetical to reliability, such as cost optimization and other things the new failure case was introduced by lots of sub optimal changes. The result is as we see it -- a catastrophic failure which caught everyone by surprise.

It's the kind of thing that happens over and over again when the accountants are in charge.