I have noticed that with some shows the file extension is incorrect and will be a set of numbers like .1427, .1425 etc. If I manually change the extension to .mkv, then Sonarr will finish the post process successfully and there are no issues with playback. I am wondering if anyone else has seen this behavior.
Also if there is a way to exclude a certain file extension or prioritize certain indexers over another to prevent this issue. Ideally since the incorrect file extension are not all the same, if there was some way to exclude numbers from the file extension would be best.