This is 100% repeatable for me. I get approximately 4 or 5, less than 10 second power failures per month (joys of regional beach living). Every time the power goes out the qbittorrent.conf file is left with 0bytes. I have to manually restore a backup before I restart the docker or all torrent files get moved into the docker. every 12 months or so I forget.
I have verified what THF13 pointed out, the qbittorrent.conf file gets written to every minute. No idea if the constant writes are required, but I do not recall binhexs' deluge docker ever doing this.
Anyway, I have a work around, but manually restoring the .conf file 4 or 5 times a month is getting old.