Ion-slider does not work properly in a modal window

modal.ts

arr = [’…/…/assets/images/11.jpg’, ‘…/…/assets/images/12.jpg’, ‘…/…/assets/images/13.jpg’];

        <ion-slides pager="true" [options]="slideOpts">
            <ion-slide *ngFor="let image of arr">
              <ion-img [src]="image"></ion-img>
            </ion-slide>
          </ion-slides>

Slider does not work properly in a modal window. For some reason the style and the pager do not show in modal windows, only if navigation is used. Is this expected because I want to scan a qr code and show a modal window with several pictures with a slider.