ionic 2 scrollToTop(300) is not working in IOS. (It was working earlier)

In my code, there is button in bottom of the screen. When I clicks on it, An automatic scroll will happen to top of the content.

this.content.scrollToTop(300);

This is working fine earlier. But now this is not working in IOS mobiles.

IONIC CLI - 3.13.0

local packages:
    @ionic/app-scripts : 1.3.8
    Cordova Platforms  : android 6.3.0
    Ionic Framework    : ionic-angular 2.3.0