Your FAEC #10
Description
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.