Mustn’t call sanitize_text_field on $_GET as whole

Throughout woocommerce-sea.php, sanitize_text_field is called on (the entirety of) $_GET. That is, repeated:

sanitize_text_field($_GET)

But $_GET is an array, and sanitize_text_field expects a string.

Which causes that function to only return the empty string: See the first lines of the actual filter it calls, _sanitize_text_fields:

if ( is_object( $str ) || is_array( $str ) ) {
    return '';
}

Either $_GET needs to be accessed with a key (not suitable) or checked through other ways, like filter_var{_array} or array_map.