I expect that this mount is a part of local-fs.target, so qbittorrent
and other processes started from user session should be stopped already.
Unfortunately i don't know what the local-fs.target is. Quick search shows that it is probably a part of systemd, which (local-fs.target) is, i guess, responsible for mounting/unmounting partitions?
Is lingering enabled in logind for the user running qbittorrent?
LIngering? Logind..?
Don't know about it either. After quick research I can say that /etc/systemd/logind.conf is the default one.