There are some bug fixes in the next version that may apply here. There is a beta for it if you would like to try it now:
Otherwise, it will be in Microsoft Store within 2 weeks. In the meantime, as a workaround, you can try converting the audio file to WAV. You can do that in Shotcut by opening it the Source player (do not add to Timeline or Playlist) and using Export with From=filename and the audio/WAV preset.