This has been a bug the last two or so versions. Sometimes I'll start the beta on the iPad or iPad Mini and the filing cabinet will be selected, but the contents of the next pane over will be Folders.
There's no way to show categories. Selecting Folders shows the next to panes over as empty.
The only fix I've found so far is to force-quit and restart the app. Not ideal.
All data is still accessible. If I use the built in browser to visit a site for which I've stored details, I can still recover those details and access the site, but there's no way to add new details, see entries, etc.