I work in software development and I’m perfectly aware of all the complexities and delays involved. However, when faced with a plausible claim about a severe vulnerability in your service, you take it down first to prevent further damage/abuse and then investigate what to do to remedy the situation. The absolutely first thing to do is to stop the bleeding.
It also depends on how many people Apple has working on filtering legit from non-legit (user ignorance) issues, before escalating.
For example, Apple might have bad resource management (only assigning only few people to filter the many many daily incoming issues 'crying wolf') and it was sitting in the queue for 3 or 4 days before escalation to qualified engineers to assess the priority.