Audio Audio Mixer groups not working

I am using Unity 2018.4.7f1 LTS and having troubles with the audio mixer.
When I create 2 child groups of the master channel, they do not appear as
a possible selection in the output for the audio source (only the master shows).
Is there a button to enable them to appear there or is this a bug?

https://gyazo.com/8119a90087a33fc834c78985b7f16329