Product Filter doesn't show the widget in the search page
The search page is not a standard section of the theme. Many developers customize this page in their theme making it difficult the use of the filters by the plugin ajax product filter.
For us it is not so easy to give support for all available issues and for that reason we have decided to disable the plugin on this page, this is why you do not see the filters in the search page.
However, although we do not support this features, and do not provide support in this regard, many users regularly use the filters on the search page. If you want to make a test then you just go and put this code in the functions.php file of your theme:
add_filter( 'yith_wcan_is_search', '__return_false' );