What I think is probably happening is that these backups were created using the old connection to Dropbox.
The main thing that has changed recently around the Cloud Backups add-on and Dropbox is that we needed to re-register a new connection with Dropbox. This means that the original connection had to be broken, however your sites should still be available for manually restoring them using Restic.
You can read more about what the original issue was, and why we needed to fix the connection between Cloud Backups and Dropbox here:
In preparation for this transition, we emailed users that were already connected to Dropbox and asked them to download a backup of their site since this was the easiest way to get a site down and into Local.
Now that the transition has been complete, Local doesn’t have a way to access those old backups, however you can still restore a site manually using Restic by following the steps outlined in this help doc: