Ok I think I figured this one out. I'm using the GitHub GraphQL API, and was adjusting some overly conservative pagination limits so some folks with a ton of repos can see all of theirs listed. Turns out I went a bit overboard and went past the limits GitHub had set in place.
Shipping a fix now, should be up in a couple of minutes (if only I could use Reflame to build the backend of Reflame... maybe one day...).
Something to check: When I click the button "Let's create your first app", I get "Oh no, something went horribly wrong!"