Cannot read property 'code' of undefined

After update Magento to it latest version 2.2.6 I've got the following issue:

Preconditions

1. Magento 2.2.6
2. PHP 7.1
3. MariaDB 10.2

Steps to reproduce

1. Add an item into the cart.
2. Open Chrome devtools console.
3. Go to checkout

Expected result

1. That checkout page doesn't display any console error.

Actual result

1. The following (down below) console error is appearing in devtools console.
   Uncaught TypeError: Cannot read property 'code' of undefined at UiClass.initialize (/en_US/Magento_Checkout/js/view/progress-bar.js:31:93)

This wasn't happening in v2.2.5
I've updated Mageplaza - OSC to latest build 2.6.1 ( https://www.mageplaza.com/changelog/m2-one-step-checkout.txt ) but doesn't fix the issue.

Hi Guys, I've found that that issue is related to the code in file /Mageplaza/Osc/view/frontend/web/js/view/shipping.js
line 97 -> stepNavigator.steps.removeAll();

You can see that in new release there're a lot of changes in cart and checkout: https://devdocs.magento.com/guides/v2.2/release-notes/ReleaseNotes2.2.6CE.html

[vetshopdeveloper]

Can confirm same issue as well

[datvm231]

Hello,

One Step Checkout is a paid extension so we have a support system here:
https://www.mageplaza.com/contact.html
Please send your problems and our technical team will help you solve it.