Add the domReady! statement

The jquery selector sometimes (depending on the amount of javascript
files) returns no values because the DOM is not ready when the script is
executed.

By adding the domReady! statement in the require part we are sure that
when the jQuery selector is being filled the DOM is ready.

app/code/Magento/Checkout/view/frontend/web/js/view/configure/product-customer-data.js

@@ -1,6 +1,7 @@
 require([
     'jquery',
-    'Magento_Customer/js/customer-data'
+    'Magento_Customer/js/customer-data',
+    'domReady!'
 ], function ($, customerData) {
     'use strict';