Hi David,
If the automatic backups are completing, then they will be stored in the same location in Dropbox.
You can check the status of the backups in the Existing Backups tab. Automatic backups are labelled as such. Does the backup appear in the list?
If so, could you send us a copy of the backup log? This will be too long to post directly, but you can use an online service to share the file and post the link here. You can also set the reply to private.
Best Wishes,
David N