–tempdir recommends the TMPDIR environment variable as being more complete,
First find it. Can you use the find command, e.g. with -ctime, to find changed files? You could get fancy if desired, and add additional qualifiers to that, e.g. -size +10M to set a size cutoff…
Or if you suspect it’s all in the temporary directory, try an ls -lcrt or similar there.
Duplicati-named files will begin with dup-, but it’s not clear what’s inside one from its filename, however one can test them, e.g. if a zip program opens it, it’s a zip file, etc. Or maybe the file command can help.