Drupal upgrade bombing out

I have tried multiple times to upgrade from d7 to d8 and it consistently bombs out after “Upgraded URL aliases”

The error message I get:

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /batch?id=23&op=do_nojs&op=do
StatusText: OK

Any ideas?

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/21/feed