Add to Cart Button – Fix Redirecting to Checkout Page Issue

Javascript error. JQuery(...).ajaxForm is not a function is what I see in the developer console.

You likely have extension conflict with that latest addition.

Change your js code with default magento code as below

var productAddToCartForm = new VarienForm('product_addtocart_form');
            productAddToCartForm.submit = function(button, url) {
                if (this.validator.validate()) {
                    var form = this.form;
                    var oldUrl = form.action;

                    if (url) {
                       form.action = url;
                    }
                    var e = null;
                    try {
                        this.form.submit();
                    } catch (e) {
                    }
                    this.form.action = oldUrl;
                    if (e) {
                        throw e;
                    }

                    if (button && button != 'undefined') {
                        button.disabled = true;
                    }
                }
            }.bind(productAddToCartForm);