I have Sonarr installed on my machine alongside SABnzbd & Plex all updated to the latest releases. I can add new shows to Sonarr and sure enough it will search and send to SABnzbd. Once completed SABnzbd moves the files to a completed Sonarr downloads ready for Sonarr to carry out the post processing. It’s here where Sonarr falls down, it will not search the Sonarr folder, copy, rename etc.
Completed Download Handling is enabled.
Below are a few screenshots to show various settings / folder locations.
Sonarr Download Client
Download drive folders