Export e-mail failures

I am trying to export e-mails from my Inbox. All e-mail titles appear, sometimes in duplicate or triplicate. However, about two-thirds of the e-mails have sizes of zero kb and have no content. This problem occurred on all three attempts I made. Any ideas?

If you open the original Inbox version of one of these failed exports, how does it appear? Is it also empty?

If it appears OK, if you export just that message, does it export OK?