Comment from vdubyna, posted on GitHub Jan 10, 2017

@astorm, @antonkril We detected the same problem on 3g connection (to replicate, you can switch the connection in developer tools) We've fixed it by adding 'domReady!' (http://requirejs.org/docs/api.html#pageload) dependency to the libraries which depend on the source code. Example: vendor/magento/module-checkout/view/frontend/web/js/model/quote.js So, after the fix, it looks like this define( ['ko', 'domReady!'], function (ko) { //... });