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)
It sucks to say this but you need to ditch that tracker.
Those files are malware. Yes it would be great if there were some mechanism to block that specific malware (there is, use your computers anti malware) but the long term fix is to go away from where they’re distributing malware.
The whole point of distributing files like that is that people like you have automated systems that go to public trackers and grab the first thing they see that matches and extract it. .arj files can have a link in them to some payload and suddenly your wonderful home server has infected itself with malware.
Time to switch to private trackers.