A few ideas based on past experiences:
1. boys in my races tend to be much more likely to stop watches or cover their bib number in a pose as they finish which is probably the largest contributor to a missed read
2. could the boys chip have been read while cheering for the girls so it didn't read because it already had read earlier?
3. boys in my races tend to be much more likely to bunch up and sprint finish where the girls tend to gap each other earlier in the race... means more congestion and faster finish, either of which can contribute to a miss.