Node.js script stops without any error

I've written a scraper using the scraper module and the queue function of async module.

I read the list of URLs to scrap from a json file and write the informations in another JSON file.

This is my script:

var fs = require("fs");

var scrap = require("scrap"),
    async = require("async");

var errors = [];

// Queue a list of URLs
var queue = JSON.parse(fs.readFileSync("products.json", "utf8"));
var len = queue.products.length;

var q = async.queue(function (url, done) {

    scrap(url, function(err, $) {
        var product = {};
        product.name = $("#page-body h2").first().text().trim();
        product.myarr = [];
        product.picture = $(".content img").first().attr("src");

        try {
            if (product.picture.indexOf("someword") > 1) {
                delete product.picture;
            }
        }
        catch (e) {
            console.error(e);
        }

        $(".content [style^=\"color: #\"] [style=\"font-weight: bold\"], .content [style=\"font-weight: bold\"] [style^=\"color: #\"]").each(function() {
            product.myarr.push($(this).text().trim().toLowerCase());
        });

        if (product.myarr.length) {
            fs.appendFile("products-parsed.json", JSON.stringify(product) + ",\n", function (err) {
                console.log(queue.products.indexOf(url), len, err);
                if (err) { errors.push(queue.products.indexOf(url)); }
                done();
            });
        }
    });

}, 20);

q.drain = function() {
    console.log(errors);
};

q.push(queue.products);

When I run it, after about 3.000 pages, it stops (quit) and it does not give any error, I have to start from the latest worked page using:

q.push(queue.products.slice(lastWorkedPage, queue.products.length - 1));

How can I fix this problem?