Hi,
We've noted a few things when looking into this:
- we haven't changed Chateau in over a year
- the tagline is shown in the screenshot of the theme description on the Theme Showcase page, and Chateau always displays site descriptions unless it’s empty in General Settings of your dashboard
- the tagline is empty in the en.blog annoucement here
I see that you have the value bundle which includes the Custom Design upgrade, so assuming you'd like to keep the tagline in Settings -> General, If you'd like me to help hide that part, please let me know and I can see if we can hide it by editing your CSS in Appearance -> Custom Design -> CSS.