Why css animation does work in Angular8 custom component?

I have a app-transition-group component that I want to animate. In my css, I have:

.flip-list-move {
  transition: transform 1s;
}

Though it appears when shuffle is called, it always changes instantaneously and never animates with angular8. It works in angular2. What is the issue?

My code is this:

app.component.ts

@Component({
  selector: 'my-app',
  template: `
    <h2>Items reorder/shuffle animations with Angular8 ngFor</h2>
    <button (click)="shuffle()">Configure</button>
    <ul [transition-group]="'flip-list'">
      <li *ngFor="let item of items" transition-group-item>
        
      </li>
    </ul>
  `,
})
export class App {
  items = [1, 2, 3, 4, 5, 6, 7, 8, 9];

  shuffle() {
    this.items = this.shufflestuff(this.items)
  }
}

shufflestuff=function(array) {
  const length = array == null ? 0 : array.length
  if (!length) {
    return []
  }
  let index = -1
  const lastIndex = length - 1
  const result = this.copyArray(array)
  while (++index < length) {
    const rand = index + Math.floor(Math.random() * (lastIndex - index + 1))
    const value = result[rand]
    result[rand] = result[index]
    result[index] = value
  }
  return result
}

copyArray=function(source, array) {
  let index = -1
  const length = source.length

  array || (array = new Array(length))
  while (++index < length) {
    array[index] = source[index]
  }
  return array
}

I have modules imported, and in my transition-group.ts file I have:

import { Component, ContentChildren, Directive, ElementRef, Input, QueryList } from '@angular/core';

@Directive({
  selector: '[app-transition-group-item]'
})
export class TransitionGroupItemDirective {
  prevPos: any;
  newPos: any;
  el: HTMLElement;
  moved: boolean;
  moveCallback: any;

  constructor(elRef: ElementRef) {
    this.el = elRef.nativeElement;
  }
}

@Directive({
  selector: '[app-transition-group]'
})
export class TransitionGroupComponent {
  @Input('app-transition-group') class;

  @ContentChildren(TransitionGroupItemDirective) items: QueryList<TransitionGroupItemDirective>;

  ngAfterContentInit() {
    this.refreshPosition('prevPos');
    this.items.changes.subscribe(items => {
      items.forEach(item => {
        item.prevPos = item.newPos || item.prevPos;
      });

      items.forEach(this.runCallback);
      this.refreshPosition('newPos');
      items.forEach(this.applyTranslation);

      // force reflow to put everything in position
      const offSet = document.body.offsetHeight;
      this.items.forEach(this.runTransition.bind(this));
    })
  }

  runCallback(item: TransitionGroupItemDirective) {
    if(item.moveCallback) {
      item.moveCallback();
    }
  }

  runTransition(item: TransitionGroupItemDirective) {
    if (!item.moved) {
      return;
    }
    const cssClass = this.class + '-move';
    let el = item.el;
    let style: any = el.style;
    el.classList.add(cssClass);
    style.transform = style.WebkitTransform = style.transitionDuration = '';
    el.addEventListener('transitionend', item.moveCallback = (e: any) => {
      if (!e || /transform$/.test(e.propertyName)) {
        el.removeEventListener('transitionend', item.moveCallback);
        item.moveCallback = null;
        el.classList.remove(cssClass);
      }
    });
  }

  refreshPosition(prop: string) {
    this.items.forEach(item => {
      item[prop] = item.el.getBoundingClientRect();
    });
  }

  applyTranslation(item: TransitionGroupItemDirective) {
    item.moved = false;
    const dx = item.prevPos.left - item.newPos.left;
    const dy = item.prevPos.top - item.newPos.top;
    if (dx || dy) {
      item.moved = true;
      let style: any = item.el.style;
      style.transform = style.WebkitTransform = 'translate(' + dx + 'px,' + dy + 'px)';
      style.transitionDuration = '0s';
    }
  }
}

How can I get this to animate when the button is hit? Stackblitz here: https://stackblitz.com/edit/angular-so-1-t81c8l?file=src/app/app.component.css

from Why css animation does work in Angular8 custom component?