Upfront Builder will not load after Update...

I have a multisite network setup and recently I seriously modified the 'Fixer' theme with upfront to create my membership site. I trashed a bunch of pages and renamed others and of course added my content.

Then I had an update for Upfront and now when I use the new version, Upfront will not load. It shows my home page and has this URL in the address bar:
http://membershipsitestarter.com/?editmode=true

But the editor never loads. If I click on the new menu link: Upfront> Builder> Modify current theme it will sometimes load the theme for editing but of course none of my modified pages are included in the 'Layout' list and sometimes it just loads a blank (white) page and stops without loading the editor.

I have deactivated all plugins and added them back one at a time and nothing seems to fix this issue. My website seems to be intact still but I can no longer edit its pages with Upfront.

Switching themes of course does nothing since I only have one upfront theme activated.

All themes and plugins are up to date. Please help me to fix this issue as soon as possible. I have granted you access via the WPMU DEV support dashboard plugin.

Thanks,
Phillip Brewer