Fade In from or fade out to black in a custom scene

[Lihinel]

Solved.

The problem was not with the fade from or to black.

I had a conditional statement like

if( x > 1000){SceneManager.goto(Scene_YYYY)}

that was not within the

if (!this.isBusy()) {
...
}

block.

I guess next time I should provide the entire code, although I didn't think anyone would read through 300-1500 lines.
Took me some time to find this, only did by reducing the working and non working Scenes down to a barebone construct and repeatedly trying if they still worked or not, guess thats one way to improve.
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So I figured it's possible to fade in a scene from black by adding this.startFadeIn(...); as the last command of of the start method after initializing some sprites so they'll appear as the black sprite fades:

Scene_XXXXX.prototype.start = function() {
.....

this.startFadeIn(this.fadeSpeed(), false);
}

However, I am not sure about about fading out.
I tried adding the following:

Scene_XXXXX.prototype.stop = function() {
Scene_Base.prototype.stop.call(this);
this.startFadeOut(this.fadeSpeed(), false);
};

and it seems to work for some custom Scenes, but not for others.
It seems to somehow break the SceneManager.goto(Scene_YYYYY) or the terminate, or something else, though no idea what, I only know that it no longer transitions to the next Scene, if I comment the stop() out everything works fine again.

So, once again, what am I doing wrong? Thanks in advance.