Biagiotti Theme: Problem with LOGIN window

Dear All, I’m having a big issue with my website (https://kivens.com ) on the login window: when a user clicks in the “ LOG IN” button the window just disappears, even without having the username and password filled in.

I’m running the last version of Biagiotti theme, already disable other plugins and the problem continues.

Could you please help me on the resolution?

Thanks