Field-Group Tabs not displaying on product page
Kind of late to the party, but I ran into this same problem earlier today and it appears to be caused by the fact that the Field Group module hardcodes the entity types that it latches onto. 

The 1.x-dev version now includes a HOOK_field_group_content_element_keys_alter() that you can use to expose any entity type to the Field Group module.

To expose products and product variations you need to create a custom module and hook into the above alter function like this

MYMODULE_field_group_content_element_keys_alter(&amp;$keys) {

  if (!isset($keys['commerce_product_variation'])) {
    $keys['commerce_product_variation'] = 'product_variation';
  }

  if (!isset($keys['commerce_product'])) {
    $keys['commerce_product'] = 'product';
  }

}


Hopefully this will be integrated into Drupal Commerce in the near future, but for now this is the only way.

Edit You can read up on the actual issue here https://www.drupal.org/node/2842280