Missing Rec - How to ask for clarification from professor?

Hello, I just applied to graduate schools. One of the schools just informed me I won't be considered for the scholarship I applied to as my second recommender did not end up sending their letter by the deadline.

This professor is someone I've taken multiple classes with (got A's) and also mentors me for my honors thesis so I was very sad to found out this happened. I'd like to email the professor and ask what happened but in a non-accusatory way to maintain my good relationship. I was wondering how I should go about it or if I should even ask?