I had struggled with backups for weeks and weeks, until I discovered that if a backup zip was larger than 2G, the job kept aborting or saving partial files, or just saving the database (for a complete site backup). I had posted several questions on this but did not get it resolved and I finally discovered that it was a ZIP file limitation.
I switched from this plugin to another because once I started using .tar files as the backup format, the backups ran properly.
Does this plugin allow .tar files, if not, will it in the future. I'd like to return to this one, but not possible with the problems I'd been having.