Background cover on ion slide doesn't work when deployed

I’ve a problem on my app with my backgrounds. On my screen when deployed my css property “background-size: cover” won’t work and images are resized like if it was translated to “width:100%; height: 100%”. Any solution ?

My html code :

<ion-content>
  <ion-slides autoplay="3000" loop="true" speed="500">
    <ion-slide id="slide1">
      [...]
    </ion-slide>
    <ion-slide id="slide2">
      [...]
    </ion-slide>
  </ion-slides>
</ion-content>

My scss code :

page-home {
  ion-slides {

    ion-slide {
      background-size: cover;
      background-position: center;
      padding-left: 40px;
      padding-right: 40px;
      min-width: 365px !important;
    }

    #slide1 {
      background-image: url('../assets/img/fond1_opacity50.jpg');
      background-position: left;
    }

    #slide2 {
      background-image: url('../assets/img/fond2_opacity50.jpg');
      background-position: left;
    }

    [...]
  }
}

On phone vs on browser :