Fatal Error with Sydney Toolbox

We received an email from WordPress letting us know that there was a fatal error on our site (https://rocaforcongress.com/). We visibly inspected our site and everything appears to be okay, but we are unable to access parts of our appearance menu for this theme. Those areas are: customize, header and background. Please let us know the steps we can take to correct this issue or if there is more info that you might need.

Thanks

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