Buttons not working correctly in Animate CC 2019

Thank you!  I didn't realize advanced layers turned all layers into symbols. While turning it off works, I'd still like to know how to get the functionality I want while maintaining advanced layers, but it does seem like advanced layers confounds or complicates some simple scripting for basic interactivity.

It seems that if you don't instantiate a button on frame 1, its button states (over, down) don't function correctly. Move any button off of the first frame, to frame 10 let's say, and you will not be able to see the "over" state on rollOver (although it seems to flash for a brief instant), regardless of any ActionScript you may have. Beyond this, let's say I wanted to get this simple AS3 code to work on a button or movieclip:

play_btn.addEventListener(MouseEvent.CLICK, onClick);

function onClick(e) {

    trace("play");

}

Using advanced layers, I can access the layer symbol with:

var myLayer = MovieClip(getChildByName("Layer_1"));

Then, I can access the button within it, using:

var myButton = myLayer.getChildByName("play_btn");  // or simply myLayer.play_btn

But, while this doesn't throw any errors, it does not work:

myButton.addEventListener(MouseEvent.CLICK, onClick);

function onClick(e) {

    trace("play");

}

Any advice on how to get this code (and/or any button or movieclip that does not reside on frame 1) to work?