I am facing the problem when I export the downloadable product in magento2 as CSV and importing the same product in magento2 it report the error that downloadable option is missing.
Magento 2 (currently up to 2.1.7) does not export the links, files and download titles of downloadable products. They are just missing in the CSV. But they are mandatory for the creation of a downloadable product.
there has to be at least one column with the name 'downloadable_samples' or 'downloadable_links'. These columns contain the downloadable information like that (just an example for an external download):
group_title=EBOOK, title=EPUB, price=12, downloads=unlimited, url=http://example.com, sortorder=1
If there are more than one downloadable items once can concat them via pipe.