I finally learned how to install qBittorrent as portable. It's amazing. Thank you for this first.
I set the completed folder outside the program, so it is not in profile\qBittorrent.
I have to say I was very impressed. It seems that the completed torrent path are saved relative to the program. So if you move both the program folder and your finished files folder into a new location and run qBittorrent, the files appear correctly in the program. (No missing files)
So the question is, how can you properly move only the completed folder into another drive for example. In that case if you run the qBittorrent, you get missing files.