I too am upgrading a shop from 1.5.6.2 to 1.7.6.1 and have found this limitation. I'm wondering if this paid module will restore the capability that used to be included in the back office for free.
Bulk Combinations Generator Module - $59.99
The current 1.7 "simplified" attributes and combinations method is unusable!
Has anybody found a workable solution?
<rant on>
When Prestashop updates software with major releases, the team should make sure all existing capabilities are maintained. Many of us Prestashop users have shops that rely on features and capabilities we don't want to lose by a software upgrade. I am upgrading from 1.5.6.2 only because it will not run under PHP 7 which I am being forced to migrate to. Otherwise, I'd be happy to stay with the Prestashop 1.5 version. I've been using Prestashop since version 1.2. The upgrade to 1.7 is the first I've needed to purchase a 3rd party data migration module to move my data. The One click upgrade process just doesn't work for me.
</rant off>