If it was a scheduling and IT problem wouldn’t this have been happening every day for months/years, and not just the past week?
A barely functioning system can stagger on for quite a long time seeming to be fine, until something perturbs it ... then it crashes to a screeching halt.
Consider a highway with very (but not overloaded) heavy traffic ... everybody is blazing along at 80 mph ... until there's a collishion ... or somebody stomps the brakes to avoid a racoon ... and the whole thing turns into a parking lot.
From what I read, the problem has been brewing for years. As they grew, it was never upgraded to handle the additional flights/routes. It worked, when they weather was nice, However the system was incapable of handling the large number of cancellations they had and couldn’t re-route/schedule crews and places so it had to be done manually. Also, it apparently never tracked crews in real time, it just assumed they were where they should be based on the schedule. Any changes had to be called in, not done on-line, leading to 4-12+ hour hold times for crews trying to get assignments. In at least one case they apparently had a crew to fly, but they system didn’t know it and they were unable to call it in to add them to the flight so it could take off.