There's just something wrong in the script. In the admin panel under 'builders' and 'field builders' you can find 3 search options : simple, quick and advanced. But the simple search is shown on the site as the advanced search. The advanced search option doesn't work.
I just changed the language key from simple search to advanced search until this error is solved.
I just changed the language key from simple search to advanced search until this error is solved.