Bug in version 4.4.1? ion-tabs not show

Ionic Framework
1

index.html

<ion-app>
<ion-nav></ion-nav>
</ion-app>

class TabsPage extends HTMLElement {
  async connectedCallback(){
    this.innerHTML = `
<ion-tabs>

  <ion-tab tab="tab-schedule">
    text example
  </ion-tab>

   <ion-tab-bar slot="bottom" selected-tab="tab-schedule">
    <ion-tab-button tab="tab-schedule">
      <ion-icon name="cart"></ion-icon>
      <ion-label>Productos</ion-label>
      <ion-badge>6</ion-badge>
    </ion-tab-button>

    <ion-tab-button tab="tab-speaker">
      <ion-icon name="contacts"></ion-icon>
      <ion-label>Speakers</ion-label>
    </ion-tab-button>

    <ion-tab-button tab="tab-map">
      <ion-icon name="map"></ion-icon>
      <ion-label>Map</ion-label>
    </ion-tab-button>

    <ion-tab-button tab="tab-about">
      <ion-icon name="information-circle"></ion-icon>
      <ion-label>About</ion-label>
    </ion-tab-button>
  </ion-tab-bar>

</ion-tabs>
    `
    const navschedule = document.getElementById('schedule')
    await navschedule.componentOnReady()
    navschedule.setRoot('tab-nav-schedule')
  }
}
async function init(){
    await nav.componentOnReady()
    nav.setRoot('app-tabs')
}
customElements.define('app-tabs',TabsPage)

document.body.onload = init

in version 4.4.1 NOT FOUND ???
Has there been any change that I have not seen in the new version?