Hi dv8info,
If those words appear in your backup report, then that means that Dropbox gave a notification that it had received the backup archive. If, in fact, Dropbox does not have it (or did have it and later removes or loses it) then that is beyond what UD is involved in. We’d have to see the backup log to check, so if you can provide that in a support thread, that’d be great. Also, we suggest checking Dropbox via their website directly – https://www.dropbox.com – as we sometimes hear in support channels from people who are looking in a device that they thought was connected and syncing to Dropbox, but wasn’t (which also is entirely “inside” Dropbox, i.e. beyond the sight or reach of UD).
If the log shows that Dropbox acknowledged receiving the file, and if it’s not now in Dropbox, then either a) Dropbox malfunctioned or b) a human being acted to delete it. If you ask Dropbox (telling them the file name) then possibly their logging will be able to tell you which of those it is.
N.B. If your site is very old, then it’s possible that your backups are in “Apps/UpdraftPlus” (https://updraftplus.com/faqs/dropbox-updraftplus-folder-changed-updraftplus-com/).
David