About the original issue, if it happens again, try to close Anki and create mpv.conf in %APPDATA%\Anki2 with autoload-files=no option to prevent automatically loading external audio or subtitle files, or download it as zip from this gist.
The %APPDATA%\Anki2 folder can be opened, for example, by clicking and editing the address bar in Windows Explorer or using Win+R or Win+S (or Win) shortcuts and pasting %APPDATA%\Anki2.
https://docs.ankiweb.net/#/files?id=file-locations
Something similar happened to me yesterday and again today. In my case, after restarting Windows and opening Anki, it could take about a minute to hear the sound for the first time, probably due to the collection.media folder containing a lot of files, slow HDD speed and high disk usage by external apps. But once it happens, the auduo seems to work fine for every new card or after restarting Anki.