SO this is the Problem Discussion:

I believe there are two main ways that Steam Recording fails to record Game Audio. The First is in your PC Settings. It is likely an Audio Device labeled "Steam Streaming Speakers" that was somehow silenced.

Second possible problem is that the game needs to hear EXACTLY what you hear. This includes all the sub-settings in your audio.

Additionally, out of reach, there may be updates that your computer needs.

As for the Solutions Discussions: [Windows]

This is what you need to checklist off:

1. Please check your Volume Mixer Settings and Reset sound devices and volumes for all apps to the recommended defaults. You can do this by going to your PC Settings > Sound > (Scroll Down) Volume Mixer > Press Reset
   
   
2. Ensure that you have NOT enhanced your audio in anyway. Go to your Sound Settings > [Select the audio device properties that you are currently using] > In the Advanced settings category, turn everything OFF
   
   
3. Are all your drivers up to date? Go into your graphics card driver hub and/or your OS and see if it requires a system update.

As for Optional Solutions:

If the above don't work, you can make do with these alternatives:

1. Change your Recording Settings to ALL System Sounds. This can be found in Steam Application by going to Steam > Settings > Game Recording > Record Audio from... > Select: All System Audio.
   
   Do be aware by doing so, it will capture ALL of your computer audio, including reviewing footage of recently captured clips, potentially leading to feedback loops of the same audio.
   
   
2. Use a Third Party application to align your Main Audio Device with the same as the Steam Streaming Speakers. You can use a free software like VoiceMeeter, set VoiceMeeter as the Default Audio Output, and in the VoiceMeeter application set your A1 Output to Steam Streaming Speakers and A2 to your preferred speakers.
   
   Do be aware by doing so, this will lead to marginal latency or visual to audio desync by a few frames. This is NOT recommended in competitive settings, however if you are recording audio, you can always video edit the audio to be a few frames forward to sync with your video

Steam Streaming Speakers appears for me and is typically used my Sunshine/Moonlight or Steam Link for streaming to an external device. Thank you for the hint. It seems when I stream to my TV and then turn the streaming off, this device is silenced. If I reboot or restart the Sunshine app, the audio comes back. I will play with this further.

I was wondering why this was happening, and it seems that the audio is always missing if I streamed a show to my TV earlier in the day before rebooting.