After updating my older project to 4.19.2 and confirming that AudioMixerXAudio2 is activated, the problem is gone. It’s weird because I went through these steps before on a new 4.19.2 UE project, and didn’t see the mixer activate in the output log. Only after uninstalling the engine, and doing everything from scratch did it work. Maybe I missed a step the first time. Those directions are linked in my post above. The way I was ale to see that the mixer was activated is that it gave me additional info in the output log such as:
LogAudioMixer: Display: Audio Device Output Speaker Info:
LogAudioMixer: Display: Name: Focusrite USB (Focusrite USB Audio)
LogAudioMixer: Display: Is Default: Yes
LogAudioMixer: Display: Sample Rate: 96000
LogAudioMixer: Display: Channel Count: 2 (was Mono? No)
LogAudioMixer: Display: Channel Order:
LogAudioMixer: Display: 0: FrontLeft
LogAudioMixer: Display: 1: FrontRight
This info does not show up for me if AudioMixerXAudio2 is not activated.
The only difference now is compression you may hear from .wav becoming .ogg, but that difference is negligible. The big thing is to just make sure that the AudioMixerXAudio2 is working.