I/O error only when seeding partially downloaded torrents

[Rainman]

I have read https://github.com/qbittorrent/qBittorrent/wiki/How-to-diagnose-IO-errors but to no avail.
I use version 3.3.13

When seeding partially downloaded torrents I often get I/O errors saying that a part file could not be found. I have no other problems with QBT, downloading and seeding works fine otherwise.
16.08.17 20:26 - An I/O error occurred, 'XXX' paused. XXX partfile read (/mnt/bla/blub/XXX/yyy.rar) error: file or folder not found.
The file it is missing is always the file that is the closest to the files I actually downloaded. For example, I downloaded the files 50 to 100 of a torrent containing 100 files, then it would be partfile 49 missing. Complaining about that seems strange since I didn't download file 49 in the first place.

SMART check says the HDD is fine.
I use Arch Linux and all mounted drives are owned by root user and root group which my user account is not a part of. However, the permissions are drwxrwxrwx=777
Changing the permissions to make my user acc the owner didn't work for some reasons.

Edit: I have forced a recheck of the torrent in question and it immediately started seeding again. I'll keep an eye on this.