Please could you send us a copy of the latest full backup log?
This can be found in the UpdraftPlus Existing Backups tab.
The contents will be too long to post here directly, but you can use an online service such as Dropbox or Pastebin, and post the link here.
By pure chance I noted the reply from you with a link to dropbox and hid it, but it was public for a while (and the user you mentioned most probably received a copy via e-mail.)
This is a public forum, and everything you post here gets scraped pretty fast by Google and various search engines (and probably by other bots, too).
I.e. Don’t publish things here that you don’t want the world to see. Instead, the official support people may share, say, a company contact page where you may get in touch with them directly. ( @bcrodua )