I dont know what is causing but i tried tons of fixes, i mainly use public torrenting, and sonarr and radarr are doing it.
I added *.arj and arj to the quality profile avoid list without success, and prowlarr is as torrent (i’ve read sometimes it gets confused and uses nzbget)
Or just set a “*.arj” file exclusion in qBitTorrent’s built in blacklist, (Options>Downloads>Excluded File Names) and use Cleanuperr to automatically delete+blocklist+repeat search for the torrent.