Mysteries of Delta Airlines

In late December, my girlfriend and I booked a flight to Maui for April. After booking a few other Delta flights, my girlfriend noticed that her Maui flight was not listed as one of her "Upcoming Flights" on Delta.com or in the App. Being a frequent flyer of Delta, she found this to be quite odd.

At first, she just passed it off as some sort of "technical error" that the website was having. After a few more days she decided to email Delta to see why her flight wasn't showing up on the website/app with her other "Upcoming Trips."

Delta emailed back indicating that the flight had been cancelled and that she should call customer service.

Today, she called Delta's customer service who confirmed that the flight had indeed been cancelled. The customer service representative did not know why the flight had been cancelled either, but thankfully reinstated the flight.

This entire transaction was done electronically. So, what could the possible reasons the flight got cancelled if 1) she did not cancel it, and 2) there was no cancellation email received?

Would really be interested this community's thoughts...thanks.