After a March Windows update I had some serious problems with VA thinking it could not hear anything through the microphone. After a variety of random troubleshooting steps (I'm not much of a Windows person) I finally unplugged the Rift S and plugged it back in and that seemed to settle everything. I went back to Elite Dangerous.
Just this morning, in the middle of a session, VA decided it no longer had any signal from the microphone. Unlike the last time however, I could independently verify that the microphone was working in Windows (Voice Recorder worked; Microphone test showed audio levels). I rebooted, checked drivers, etc. What did finally fix it was I disabled the Oculus Virtual Audio Device as a microphone (in Settings/Manage sound devices), and as soon as I did that, VA could "hear" again via the regular Headset Microphone on the Rift S.
I don't know where the Oculus Virtual Audio Device came from. I don't know if it was there before the March updates or not (it was several updates). AND when I re-enabled the virtual device VA continued to work. So...go figure.
Anyway, if anyone else has this problem, I recommend disabling the Oculus Virtual Audio Device as a microphone and see if VA starts working.