Answer
Check whether the Migration Job's File Location is actually set to 'OnClient' rather than a server-side location — when File Location is OnClient, the application writes the output file to the exact path entered on the CLIENT machine running the job, which can be a UNC path or a mapped network drive, as long as it's reachable from that specific client PC, not to a path on the server itself. This explains why the output doesn't appear on the server folder expected, and also why there's no dedicated screen to pre-register new server-side paths — an OnClient path is simply typed in directly rather than selected from a managed list.