component.html

<div class="row" cdkDropListGroup>
  <!-- NOTE that each item gets its own cdkDropList, then we treat it as a series of different cdkDropLists. -->
  <div *ngFor="let item of items; index as i" 
       class="col-6 col-md-4 col-lg-3 mb-3" 
       cdkDropList 
       [cdkDropListData]="i"
       cdkDropListOrientation="horizontal">
    <app-item [item]="item" cdkDrag (cdkDragEntered)="entered($event)" (cdkDragEnded)="ended($event)" [cdkDragData]="i">
    </app-item>
  </div>
</div>

component.ts

lastFrom: number;
lastTo: number;

constructor(private cd: ChangeDetectorRef) { }

entered(e: CdkDragEnter) {
  if (this.items && this.items.length === 1) {
    return;
  }

  this.lastFrom = e.item.data;
  this.lastTo = e.container.data;
}

ended(e: CdkDragEnd) {
  if (this.items && this.items.length === 1) {
    return;
  }
  if (this.lastFrom === undefined || this.lastTo === undefined) {
    return;
  }
  moveItemInArray(this.items, this.lastFrom, this.lastTo);
  this.cd.detectChanges();
}

Updated to handle some corner cases.