From @akamura on July 28, 2016 20:16

Preconditions

1. PHP 7.0.6
2. MySQL CE 5.6.30
3. Magento 2.1.0

Steps to reproduce

Create a CSV with 3 virtual products and one configurable product.
The only attribute configurable is COLOR.
Add to the CSV (screenshot attached) the additional_attributes field, as well as configurable_variations and configurable_variation_lables.

Expected result

The import procedure should create three virtual products and one configurable and using the configurable_variations and configurable_variation_labels connect the three virtual products to the configurable one.

Actual result

Imported file:

Exported file:
As you can see Magento ignore both configurable_variations and configurable_variation_labels fields making the import successful but configurable products fail.

Copied from original issue: magento/magento2#5876