When I open the checkout page the ZIP code field is already validation failed. The field doesn't have a value. It doesn't occur every I open the checkout page.
I noticed this with two different Magento 2 environments. One is version 2.1.0, the other one is 2.0.7. It doesn't matter which theme I'm using, it occurs with the blank theme as well. I'm using Dutch locale.
That mean shipping address data is empty.
You can check it on Magento_Checkout/js/view/shipping.js at line **103**
I have insert
null != shippingAddressData.postcode
And this bug was fixed. Please make sure all case work.
if (shippingAddressData && null != shippingAddressData.postcode)