In this case, a client possessing seasonal contracts used an enterprise resource planning (ERP) system that could only hold a single schedule at any one time. As a result, this meant that on October 1, literally all schedules would have to change overnight.
Unfortunately, the software used was set so that schedules were intended to be uploaded via user interface (UI) and were not done so successfully. This created a spike of work that needed to happen in a few hours.