MacBook Pro with Touch Bar - muted until I tap the volume slider?

I've been encountering a behavior on my 2020 MacBook Pro with the Touch Bar. What I'm finding is that if I launch a page that has video, the video is muted. Sometimes the site does this and requires tapping on on-screen volume control. But in cases where the site doesn't automatically mute the audio, I find I have to tap the volume soft button on the Touch Bar and then tap the slider -- anywhere really -- to get audio. I've verified (several times) that the MacBook isn't muted in the first place -- I'll be listening to music, stop the music an open a web page with video, and find myself muted again.

I suspected at first this might be a side effect of installing Blackhole to capture audio from a web video - but even after completely uninstalling Blackhole the issue persists.

This appears to be entirely repeatable.