Stuck here for the last 2.5 hours
There is a 5 GB limit for backups to Amazon S3 where we store the .zip files, so I expect you might be hitting that limit. The best work-around for now is to use the Mac app to export, since it can save directly to your hard drive.
Ah! Doing it now. I forget about the Mac app for such purposes. Also, like that it has a progress bar.
Update: It was 3.8 GB and took quite a while to compile on the Mac app.