Expanding multiple rows in a nested mat table in Angular not working

The expand/collapse logic is quite similar as in the answer for How to expand multiple rows in a Mat Table on clicking of a row in Angular?.

Concepts (TL;DR)

1. toggleElement function to Add element to expandedElement.
2. isExpanded function to Check element is existed in expandedElement.
3. Display element (is expanded/collapsed) with isExpanded.

SOLUTION

Previous

<div class="example-element-detail" *ngIf="element.addresses?.data.length" [@detailExpand]="element == expandedElement ? 'expanded' : 'collapsed'">
  <div class="inner-table mat-elevation-z8" *ngIf="expandedElement">

<tr mat-row *matRowDef="let element; columns: columnsToDisplay;" [class.example-element-row]="element.addresses?.data.length"
     [class.example-expanded-row]="expandedElement === element" (click)="toggleRow(element)">
</tr>

As the element is added into expandedElements to represent it is expanded, thus you need to check whether the element is in the expandedElements with isExpanded(element).

Latest

<div class="example-element-detail" *ngIf="element.addresses?.data.length" [@detailExpand]="isExpanded(element)">
  <div class="inner-table mat-elevation-z8" *ngIf="isExpanded(element)">

<tr mat-row *matRowDef="let element; columns: columnsToDisplay;" [class.example-element-row]="element.addresses?.data.length"
     [class.example-expanded-row]="isExpanded(element)" (click)="toggleRow(element)">
</tr>

.component.ts

export class TableExpandableRowsExample {

  ...

  expandedElements: any[] = [];

  ...

  toggleRow(element: User) {
    element.addresses && (element.addresses as MatTableDataSource<Address>).data.length 
      ? this.toggleElement(element) 
      : null;
    this.cd.detectChanges();
    this.innerTables.forEach((table, index) => (table.dataSource as MatTableDataSource<Address>).sort = this.innerSort.toArray()[index]);
  }

  isExpanded(row: User): string {
    const index = this.expandedElements.findIndex(x => x.name == row.name);
    if (index !== -1) {
      return 'expanded';
    }
    return 'collapsed';
  }

  toggleElement(row: User){
    const index = this.expandedElements.findIndex(x => x.name == row.name);
    if (index === -1) {
      this.expandedElements.push(row);
    } else {
      this.expandedElements.splice(index, 1);
    }
  }
}

Sample Solution on StackBlitz