marionette js -- Fails after upgrading Jquery to 3.4.1 from 1.11.1

Question

In an old legacy project created with backbone and marionette 2.4.1, we were using jquery 1.11. Due to security scan, we are asked to upgrade to latest JQuery. But after upgrading, the pages are not showing up.

To be more precise, the render method (of class extended from Marionette.ItemView) does not get executed.

    var HeaderView = Marionette.ItemView.extend({
            //el: $('nav#header > div.container-fluid'),
            template: _.template(UserTemplate),
            ...
            ...

Not only render(), but none of the other methods like onRender, onBeforeRender etc., also not invoked. I can see in the logs that only an initialize function gets executed.

The HeaderView is a child of AppLayoutView which is derived from Marionette.LayoutView. The last thing I see in the logs is that AppLayout.onRender() is invoked, followed by initialize method in this HeaderView.

There is no error in the web console of any sort, except for few warnings that used to come earlier.

I know this is a very generic question, and difficult to answer. But I am looking at some pointers, or if someone faced similar issue and fixed it.