In an older case of a similar failure, I wrote:
The workaround there was to not use --targetpath, but can you get away with that? Is it really 1 file?
Restoring files using the Recovery Tool gives a usage example, but I’ve always felt the help was vague:
Restore
-------
Duplicati.RecoveryTool.exe restore <localfolder> [version] [options]
Restores all files to their respective destinations. Use --targetpath to choose another folder where the files are restored into.
Use the filters, --exclude, to perform a partial restore.
Version can be either a number, a filename or a date. If omitted the most recent backup is used.
Maybe it’s just old text? I had thought it would take an --include filter, but I haven’t tested it recently. Normal options such as --dbpath and --no-encryption are likely irrelevant here but might not hurt.
A developer look at the code that I cited would be helpful. Meanwhile is it really 1 file to another spot?
EDIT:
There are some other differences too, e.g. the other case used Windows, so had a drive letter in front.
If yours is truly a backup of one file (is it?) is there a reason you’re not restoring onto the original path?
If there’s something there you want to keep, you could move it out of the way. I’m lacking context here.