It has something to do with the new drop system overcompensating, its an extreme form of an intended feature. Basically you get a bonus for every day you don't get a girl while fighting a certain amount of times on that day (and certain other conditions), and that bonus decreases when you get a girl drop. You can get a bonus that lets you get multiple in a row through that, so not everyone has it but some people do.
It's not a exactly bug, but more of an oversight that creates this situation if you can't get girls for an extended period of time.