iOS 10 and later requires your approval to access the recordings in iTunes. The first time you run Set List Maker on iOS 10, it will prompt you to approve access to the media library. If you decline, all the recording buttons in Set List Maker will be disabled and nothing will appear in the Add Recordings window.
The solution in this case is to open the Settings app, go to Privacy > Media Library > Set List Maker, and manually enable that setting.