In my Unreal project (4.18.3) the audio is working fine while playing in the editor, but doesn't work (it's completely silent) in a Shipping build.
If I use the Vive instead of the Rift with the exact same Shipping build the audio works fine, so it's definitely an issue with Oculus.
I have tried running the shipping build from my hard drive, but have also uploaded it to the Alpha Release Channel for my project and downloaded it and played it through the Oculus store with the same result.
The build is successful, but it does include these lines in the Output Log, which seem like they might be relevant:
[OVRPlugin][ERROR] ovr_GetAudioDeviceInGuidStr failed:
[OVRPlugin][ERROR] Cannot get preferred VR audio IN device.[OVRPlugin][ERROR] ovr_GetAudioDeviceOutGuidStr failed:
Has anyone else experienced this, and knows how to fix it?