Dug around a little bit and traced it back to
Add support for html comments to template syntax (#3662) · ankitects/anki@ef94bf1
The Chinese support addon places the sound tag in a comment in the default card type, see:
<!-- {{Sound}}-->
This is Hyrum’s Law at its finest and feels a little tricky. The addon arguably shouldn’t be expecting tags in comments to be templatized and parsed, instead it should hide the sound field in an element with display: none… but the damage is already done.
I will open a PR updating the addon but from my work with it in the past, there might be some difficulty getting it merged due to inactivity around supporing it. There might be a large horde of Chinese learners who appear in the forums complaining their audio suddenly stopped working.