For one of my books (https://leanpub.com/author/book/fastfeedbackusingruby), generating a preview fails when attempting to push changes to Dropbox.

The error/info message is this:

This error occurred during a preview.

[AI Suggestion]
**Category: INFRASTRUCTURE**

This isn't something in your manuscript — it's an internal issue on our side. Our build system encountered a temporary communication problem with Dropbox while trying to sync your project files. Please try building again; these transient network hiccups usually resolve on retry, and our team has been notified of the issue.

Retrying, however, didn't help. I'm getting the same error again.

Generating a PDF preview for another book works fine, though. So I'm wondering what I am missing here…