Try to add the following PHP code snippet to the child theme functions.php file to fix this
add_filter('relevanssi_search_params', function ( $search_params ) {
$post_type = get_query_var( 'post_type' );
if ( false !== strpos( $post_type, ',' ) ) {
$post_type = explode( ',', $post_type );
set_query_var( 'post_type', $post_type );
}
return $search_params;
});
.
