signoutPopup() works as expected but signoutRedirect() doesn't terminate session.

[sewalsh]

  private manager = new UserManager({
    authority: this.configService.authAppURI,
    client_id: 'angular_spa',
    redirect_uri: 'http://localhost:4200/auth-callback',
    post_logout_redirect_uri: 'http://localhost:4200/',
    response_type: 'code',
    scope: 'openid profile email api.read',
    filterProtocolClaims: true,
    loadUserInfo: true,
  });

That's my UserManager object.

If I sign out through the signoutPopup() function, a popup window appears and the user is out the session (and the session in the background window).

async signout() {
    await this.manager.signoutPopup();
  }

If I use signoutRedirect(), it remains logged in.

async signout() {
   await this.manager.signoutRedirect();
  }

In the console, it shows Navigated to http://localhost:5000/connect/endsession?id_token_hint=eyJhbGciOiJS.... when the function is called but the Network inspector doesn't have any record of actually hitting that end-point.

Has anyone had a similar issue to this? Am I doing something trivially stupid?