At my company there was a service outage that lasted 2-3 weeks for a specific feature we have. This was caused by everyone quitting and no one having any experience with this service. The rest of the application remained working so it wasn't so noticable to the outside world. But internally and for customers it was massive since it was the billing system that went down.

There was another incident that took down everything that was caused by a Spring cloud config being changed that no one in the company had access to.