Exporting via Dropbox, you will see Dropbox.com Error 1001.
Exporting via wifi, the resulting file is empty (0 kb).
The csv export did work in my initial use of the app, just not now.
This error can occur when the "CSV Encoding" is incorrect under the "Settings" page (within the app). By default, it is set to "8-bit ISO Latin". It will produce an empty csv file when that encoding fails because there are characters that can't be represented by the current setting. Try setting it to another encoding until you find success.