Why would a reply not be included in the stats? It displays a black trophy next to the First Reply time

A black trophy indicates a first reply time that is either excluded from the average First Reply Time displayed at the top of the report because it was the customer’s first reply time (and not a First Reply from one of your team members) or because there’s an active filter which is excluding that particular email.

The date filter is also taken into account when displaying replying times that are included or excluded from the average First Reply Time displayed at the top of the report.