I recently experienced this problem, all my apps on UWP no longer play any sounds. I traced the problem to this line of javascript in the c2runtime:
useOgg = !!(new Audio().canPlayType('audio/ogg; codecs="vorbis"'));
It looks like if your windows installation has the audio pack that supports .ogg the audio system attempts to use .ogg audio files. However, the default export for c2 UWP projects is to use .m4a. So, what is happening is the the .ogg is not present and so we get 404 errors which silently error and send an empty sound data array to the audio decoder.
It should be fixed if you add the .ogg versions of your audio files to the exported media library.