Sadly, that was not the case. That was my first scene, no instantiate. I don't know if this has been fixed or not. AFAIK, I want to achieve reusable AudioStreamPlayer, instead of using a lot of AudioStreamPlayer, I can use only one AudioStreamPlayer and change the stream (clip).
The sfx is not null, I've tried to check it with print(sfx)
this might be easy fix with this issues, just load at _ready(), something like
audio_sfx = load(audio_sfx.resource_path)
Well, I haven't tried it anyway, haven't in touch with that again.