A not-auspicious occurrence is a scandal. A scandal is pretty much the opposite of an auspicious occurrence.

不祥事 refers to a scandal that brings about dishonor, particularly to institutions, organizations, or public figures. It often involves misconduct, corruption, or other unethical behavior that has a significant negative impact on their public image.

This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.