For those of you trying to perform the export and failing to do so, note that when you execute "Export" from WebUI, after creation of the archive completed, which is indicated by the message and the progress bar status, there is a noticeable pause before "Download" button appears in the dialog box.
If you do not see it, wait and DO NOT click on "OK", as this will nullify the export procedure.
After some 30 seconds to a minute, the "Download" button appears in the same dialog box and you can proceed with it.