CMS - Unable to open assets

Our CMS, which runs google apps scripts in an iframe, was not loading documents, known as "assets" - I thought maybe that the google apps script is not running? Or seems to be returning a blank page?

But the next day, it was fine. (In fact, when I tested the previous day, I had logged in to multiple accounts, which is probably why it didn't work. We need to be logged in to only one google account for the google apps script to work correctly. So, opened in a private window today, and it works.)