Problem whit Sydney Theme

I’m having an issue with the display of the Sydney theme. When I make changes in the customizer, they are not being applied.

For example, the headbar is supposed to be white, with blue menu text and a button on the right, and the footer is set to have a blue background — but when I save the changes and return to the theme, none of the modifications are taken into account.

I’ve already contacted my web hosting provider, but they told me it’s not an issue on their end.

Moreover, I tried using a different theme, and this problem didn’t occur, which makes me think it’s a settings-related issue — but I don’t know exactly what or where to look.

Do you have any suggestions?

The page I need help with: [log in to see the link]