mat-checkbox restore SelectionModel using HttpClient Observable

I want to restore the mat-checkbox selection using http Observable stream. The selection is not reflected on the page.

Below is the structure of the code. A mat-table with first column containing the checkbox column.

html

-- Checkbox is first column of mat-table
<table mat-table [dataSource]="fixture.dataSource"
 <!-- Checkbox Column -->
  <ng-container matColumnDef="select">
    <th mat-header-cell *matHeaderCellDef></th>
    <td mat-cell *matCellDef="let row">
      <mat-checkbox (click)="$event.stopPropagation()"
                    (change)="$event ? fixture.selectionModel1.toggle(row) : null"
                    [checked]="fixture.selectionModel.isSelected(row)"
                    [disabled]="fixture.selectionModel.selected.length >3 && !fixture.selectionModel1.isSelected(row)">
      </mat-checkbox>
    </td>
  </ng-container>

component.ts

this.fixture.dataSource = this.route.snapshot.data['fixtureresolver']
//structure of fixture object
fixture ={
    dataSource = [some data]
    selectionModel = new SelectionModel<Player>(true, [])
}

e.g. I have saved checkbox selection in monogdb from where I will retrieve the row identifier using httpclient, however just for sake of testing, i am first simply trying to select all the checkboxes by passing the row from the dataSource into the SelectionModel.select(row) function.

fixture.selectionModel.clear()
fixture.dataSource.subscribe(ds1=>{

 ds1.forEach(row => {
 fixture.selectionModel.select(row)
 });
})
this.cdr.detectChanges()

Here is how selectionModel object looks on page load. It shows that _selected has 23 rows, but does reflect on the UI. However the [disabled] constraint is working as all checkboxes are in disabled state