Feedback score dropped by +1

Yesterday I had a feedback score of +793. Today I logged onto the system and my feedback had dropped to +792. I immediately assumed someone had left me negative feedback, but when I looked at my feedback, there were no negatives and no neutrals. In fact, my recent feedback looked exactly the same as it had the day before except that the feedback score had dropped by +1.

How does a person's feedback score drop by +1 if there are no negative or neutral feedbacks, and the recent feedback appears unchanged?

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