There is no bug. Somehow i solved it. I only use godot for a few days, this is my first game, so i don't really know what i did.I use buses too, with no effect because....
On run time, the first sound that played (very loud and too scary for a baby game) was the one selected in the Inspector - Stream. I tryed to change the stream, with ANOTHER one, from inside the script in ready function, but the FIRST scary sound did not stoped. (After the scream, the "another" was used ok.)
Then i realized that, in the same script,
in ready function
i autostarted a Timer (the one that emited that sound on timeout) before set the AudioStreamPlayer.stream="" (maybe the bus too?) , so the one that played was the one from the Inspector without the bus limiter or volume set. I was sure that 3 seconds on timer will be ok time to load the stream and bus, but....
So , make sure that on runtime
first AudioServer.set_bus_layout(something_bus) (in another parent node ready funct, in my case)
then set audioelement.stream = "something_stream" (in ready function)
only then started the timer (or other things ) that call to soundname".play" the sound on some timeout, etc , just to be sure it does not scream any more. (in the same _ready function)
(at first, in panic, i erased the stream from the inspector, but now it does not matter if is there or not)