Adding Sound will stop the SoundChannel through the buffer during the close method execution.

[rainyt]

Fixed the issue where SoundChannel may cause SoundMixer to close during playback the __soundChannels array will not be removed, ultimately causing the audio to reach its maximum limit and unable to play the audio.

Like this:

var sound:Sound = openfl.Assets.getSound("assets/sound.mp3");
sound.play();
sound.close();
// The audio length is 1, but the correct value should be 0. 
// After the audio is turned off, you will never receive an audio playback completion event.
trace(@privateAccess SoundMixer.__soundChannels.length);