Upfront not loading and upgrading WPMU didn't help

We installed WPMU and Upfront Builder more than a year ago and have been using it since. A little while ago, it stopped working and would staying on ‘loading…’ forever. When going to the WPMU dash it said we had to upgrade, so I did and paid. Now I can see the WPMU dash, but Upfront doesn’t show in installed plugins even though it -is- available as menu at top left menubar in WP and tries to load.

I need to understand how to upgrade and install upfront without trashing current pages.