First step is probably to find out which file is missing. Watch About → Show log → Live → Warning fail.
<backup> → Show log → Remote might be able to awkwardly see whether Duplicati tried to do upload.
Is this an initial backup or one with long history on it that failed? Anything unusual in job logs around then?
Because your stack is in PreBackupVerify, whatever went wrong probably went wrong on prior backup…
If problem is easily reproducible from scratch, setting log-file=<path> at log-file-log-level=retry can debug.
EDIT:
If it’s an older backup, I suppose you could look for something like DB Browser for SQLite (sqlitebrowser).
Your error looks like Remotevolume table says it has an uploaded file that it isn’t seeing in Tardigrade now.
RemoteOperation table can maybe show when file was uploaded, but log file from scratch may be easier.
What happens?