Works in Animate Test but Not all works in html5

I am sure this has been asked many times but after searching I still can't find a solution.

I have created an animation in Adobe Animate that flows fine. I have set the sequnce to loop 3 times but adding this code on the 3nd to last frame.

if (!this.looped) this.looped = 1;
if (this.looped < 3) this.gotoAndPlay("start_frame");
if (this.looped++ == 3) this.stop();

Then on the last frame I show a final screen. I link to this with a button.

this.PopupBtn.addEventListener("click", fl_ClickToGoToFrame1.bind(this));
function fl_ClickToGoToFrame1()
{
    this.gotoAndStop("popup_frame");
}

on the popup frame I have a cancel button which used=s the following script:

this.cancelBtn.addEventListener("click", fl_ClickToGoToStart.bind(this));
function fl_ClickToGoToStart()
{
    this.gotoAndPlay("start_frame");
}

this all works fine in Test Mode, but as soon as I publish to html5 the canel button on the poup fails.

In the publishing settings 'Basic' I have set 'combined image into spritesheet' to off and in 'Image Settings' set this to export Image assets and also turned off combine images into spritesheet.

Why can the test work file but when I puiblish it fails?