Ionic Slide is not jumping to particular slide

Appflow
1

Hello .
In my ionic 3 project I Have my home page where I have several vertical slides . I want while page loads it should open a particular slide by its index number . I have used initialSlide property which sometimes working and sometimes does not .

How to fix this ?

newsfeed.html

 <ion-slides dir="{{dir}}" speed="300" initialSlide={{index_num}} direction="vertical" effect="flip"
              (ionSlideWillChange)="onSlideChangeStart($event)">
    <ion-slide *ngFor="let slide of rssDataArray" (swipe)="swipeEvent($event)">
      <div class="slide-image-div">
        <img [src]="slide.image ? slide.image : default_image" class="slide-image" (click)="tapOnHomePage(tap_status)">
      </div>
      <h2 (click)="saveToBookMarks()" class="slide-title" [innerHTML]="slide.title"
          [style.color]="bookmark_color_header"></h2>
      <p class="description" [innerHTML]="slide.description" (click)="tapOnHomePage(tap_status)"></p>
      <p class="tips">swipe left for more news</p>
    </ion-slide>
  </ion-slides>