A totally unexpected parent job loss. New job quickly found in the same field, but at a substantially lower salary (the salary decrease was more than the bill for a year of kid’s college). It also ate into the emergency fund which then needed to be replenished, while living on the lower salary and while the last kid was applying to college. COBRA for only two months was several thousand dollars by itself.
More recently, unexpected expensive dental work. Thousands in costs past the limits of the dental insurance.
We also had a kid get really sick while studying abroad. It came within a couple of missed classes (after being ordered by a doctor to stay home) of costing her the entire semester.
We’ve seen others have a year added to the degree because of a low passing grade in one junior year class that required a high grade as a major prereq. for several senior year classes and was only offered once a year. That added year was not covered by the student’s academic scholarship. Strong student, difficult major.