What is unique about iOS 9.0/9.1 web page loading process?

Question

I am experiencing an issue that is only reproducible in iOS 9.0 and iOS 9.1 in a Safari browser for a website we created. The page seems to take more than 15- 30 seconds to load and each touch registered is not responsive.

This is a very recent issue and we did not experience it before a certain deployment. I looked through our Git version control and the only thing that seemed to have changed was some introduction of JavaScript that animated the body. Here's a snippet.

if ($(".selector1").length > 0) {
  $('body, html').animate({
        scrollTop: $('form[name="form1"').offset().top - 10
    }, 1000);
}

This code block was wrapped around in a jQuery(document).ready(function(){//code in here}) block.

We were unable to reproduce this issue in either iOS 8.2, iOS 9.2, or any Android or Windows devices.

Has anyone experienced this issue before/have any solutions to solve it?