I'm not sure exactly how to get into this situation, but if you already have rars for a release in your PP folder, then Harpoon starts to do its thing and download/extract/delete the rars of a release, you'll wind up in a scenario wherein you've got both the rar files, and the unrared .mkv file.
After sonarr/radarr has PP'd the release, you're left with the untouched rars still. This requires manual cleanup.
I'm not sure exactly how to get into this situation, but if you already have rars for a release in your PP folder, then Harpoon starts to do its thing and download/extract/delete the rars of a release, you'll wind up in a scenario wherein you've got both the rar files, and the unrared .mkv file.
After sonarr/radarr has PP'd the release, you're left with the untouched rars still. This requires manual cleanup.