Steps:
Set up an Audio Source with audio on an avatar
Add a VRC Spatial Audio Source component to it
Set the Gain to 0 and upload the avatar
Load avatar in Audio Beta an hear that Audio Source does not play.
I created an example avatar w/ multiple Audio Sources that have different gain values for testing. All values on the VRC Spatial Audio components and Audio Sources are default except for Gain.
On Live all audio sources on the example avatar (Range 10dB -> -10dB) work, though I personally don't notice a difference in loudness
On Beta, only audio sources w/ a gain above 0 work. All other audio sources don't play any sound. Did notice the difference in loudness though.
I noticed this bug after an asset I had no longered played sound during the beta. I'm pretty sure this asset worked in the steam audio beta before this most recent update, so this might have been caused by one of the changes in the current audio beta