It is embarrassing to report that I have lost all my female students after two lectures. ;_; What did I do wrong? (Was the fault entirely mine?)

This is a delicate topic, extremely easy to offend people. I have a conjecture that my female students disliked challenges. Offence made. ;_; Please talk to me before quitting. Now I have no chance of knowing whether my conjecture is true or not.

Update:
I checked the history of the registration record. There was zero female student to start with. It was just that those who sat in left. That was natural... except it was not. (╯°□°)╯︵ ┻━┻ How could there be no female student who registered?