Good point, I am now setting the router source explicitly but I still encounter the same problem.
Any other idea on what I can check?
nginx
    location / {
        try_files $uri $uri/ @rewrite;
    }
    location @rewrite {
        rewrite ^(.*)$ /index.php?_url=$1;
    }
service
    $router = new Router(false);
    $router->setUriSource(Router::URI_SOURCE_GET_URL);
controller
    /**
     * @Get("/lft/{lft}")
     */
        public function getByLftAction( $lft  )
        {
            var_dump($this->request->getQuery());
            echo $lft;
        }
result
<b>Warning</b>:  Missing argument 1 for ..
array(1) {
  ["_url"]=>
  string(13) "/flight/lft/1"
}