Difference between events listener codes

Ionic Framework ionic-v3
5

I am extremely sorry for the spelling mistake.
I meant to type ionViewDidLoad() which I got to know form this document.

ionViewDidLoad(){
    this.events.subscribe('update-menu-title', (userInfo) => { // listener for "update-menu-title" event
        // Usage of 'userInfo'
    })
}

Also, I found out the Ionic page life cycle events will not trigger from app.component.ts because it is not a normal page. Only Angular life cycle hooks will work.
This is explained in this forum question and in this reported issue.

But, I am still unable to understand why optimized build ionic cordova build/emulate android --prod is not trigerring custom event listener if I modify my code as mentioned in point 2 in original question.