Katie, thanks for your speedy reply, but from my perspective, the problem is only half fixed.
Alphabetical order by author is still not working, using the shortcode you recommended:
[zotpress collection="M7AGPJ4D" sortby="author"]
But chronological order in descending order is working nicely now:
[zotpress collection="M7AGPJ4D" sortby="date" order="desc"]
You can see both at the link below, and please tell me if I'm overlooking something.