The issue was solved, but just in case anyone has the same issue, I had to switch off the "Enable Enhanced Composer" option in the page delivery settings, and the session loaded in the experience designer.
I'm trying to create an a-b test that involves testing a banner that only displays when a user is logged in. The banner won't display in the visual experience designer because it loads the unlogged-in user view of the page. I'm logged in to the website outside of adobe, and thought the session would...