How to fix «Cannot read property 'code' of undefined» in `Magento_Checkout/js/view/progress-bar.js`?

Issues
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The issue is fixed in Magento 2.2.8 and 2.3.1.
So to fix the issue in an ealier Magento version you can just replace the Magento_Checkout/js/view/progress-bar.js script with the version from Magento 2.3.1:

github.com/magento/magento2/blob/2.3.1/app/code/Magento/Checkout/view/frontend/web/js/view/progress-bar.js