IMPORTANT:
(TL;DR: in most cases CDH must be turned on, except with an exotic custom workflow)
I want to explain what’s happening here, because this is a recipe for disaster.
When Sonarr grabs a release, it logs that into the History and sends the nzb to the download client.
Sonarr keeps track of those downloads via the download client API. That way it knows what is still downloading and knows what is ready to be imported.
Sonarr only does this when Completed Download Handling it turned on, and it is the most reliable way to import stuff.
If Sonarr does another search or rss sync, it might run into the same or similar releases. It looks up both the existing episodefiles and the current downloads, and concludes it’s already being downloaded and won’t grab it.
Some people however have a custom setup, and don’t use Sonarr to import, instead handling it themselves.
In those cases downloads disappear into thin air, and Sonarr doesn’t know you already have that download.
Now, if CDH is turned OFF, then Sonarr obviously can’t check the current downloads. So instead it will check the History, if the last event logged in history is ‘Grabbed’ and use that as criteria instead.
So, we do not recommend you to turn of Completed Download Handling. You should have it turned on, unless when it conflicts with your workflow. In 99.9% of the cases CDH should be turned on.
If you have a normal workflow that doesn’t involved custom pp-scripts, and you have those ‘repeatedly downloading the same episodes’ then please, open a new thread where you explain your setup.
Disclaimer: The behavior described in this post is subject to change in future versions. So if you’re reading this a year from now, don’t assume it’s correct.