I downloaded a couple of stories last night that came up with the author listed as Anonymous, authornumber 0, with an authorlink that was just AO3's main page. It caught me by surprise because I tend to grab links out of other people's bookmarks pages to download, so I didn't notice at first. It was only when I tried to check the author's page for additional info that I realized something was amiss.
My best guess is that it's because the author has Japanese kanji in the authorname, though I can manually edit the Calibre metadata and the HTML of the story to paste it in. I generally keep Calibre updated, but this was before today's update. I generally keep FFF updated to the latest release, but not the latest test version.
https://archiveofourown.org/works/19908862
https://archiveofourown.org/works/20014489