When downloaded torrent files are deleted through file manager , Ttorrent app is controlling the files and after seeing they don't exist it is restarting the download. So, to solve this problem torrents should be autopaused.
If torrents autopause as soon as they complete, no seeding will ever occur. This can be offered as an *option*, but I do not recommend using it. Users who stop torrents as soon as they finish are "leeching" & if that became the norm for tTorrent users it is likely that other torrent clients would begin to block all tTorrent clients by default.