qBittorrent official forums

Can someone give a short explanation about this feature in qb?
I found a bunch of *.fastresume files in
~/.local/share/data/qBittorrent/BT_backup/
and also some config file here:
~/.config/qBittorrent/qBittorrent-resume.conf
How does it work?

I'm trying to figure out a loss of 1.3 GB torrent on seed after a system locked up. At first suspected a xfs file system, but torrent was completed (and moved from "uncomplete" folder to a "completed") for at least 6 hours at a time of the lock. It was a couple of rar archives in a folder which i extracted to a different partition and it was all fine. It was all done after torrent finished and i don't believe it to be some "delayed" feature od xfs. Never happened before and 6h is a bit too much time to be some feature of the fs (don't have any fancy mount options).
After a reboot and restart of qb this particular torrent started from scratch. Recheck didn't help. All files are gone from "completed" folder and qb started downloading again into "uncompleted" folder. My home folder is on ext4 and both torrent folders are on separate disk under xfs.

Try to check option -- "append .!qB to incomplite files". This should protect you from losing data again. Even if a torrent get corrupted, it will create new files, now with .!qB extension. If this happens again, stop all your corrupted torrents and simply delete .!qB files. Then, recheck the torrent files. They should be fine.