I've installed a brand new Drupal 8 site (http://www.edcint.co.nz/tmp/drupal8_problem_new.PNG) with next to no configuration, default theme etc. I then ran Drupal Update against a Drupal 7 site (http://www.edcint.co.nz/tmp/drupal8_problem_existing.PNG). The content/users all came across but the front page shows without any theme or blocks, only the 3 articles/pages marked as "published to the front page" appear.
I've migrated another more simple Drupal 7 site to Drupal 8 and this did not happen.
Have I hit some limitation of the Upgrade module? How can I make the theme and blocks reappear on the front page?