Apps aren't shown in the Sound Control listing until they have played audio while Sound Control is running. Try playing some audio in the app that is missing from the list and check the list again.
If this doesn't work, make sure that the app isn't in the "Ignored Apps" list in preferences.
Select the app and click on the minus (remove) button to remove it from the list. Check the Sound Control list again.
If it still isn't showing up in the list, please contact us so we can look into it.