Laravel 5.4: controller method is called twice on a redirect to it

I'm encountering a problem where a redirect from one route to another is calling the targeted controller method twice. This question addresses a similar issue, but the OP passing a 301 status code was deemed to be the issue in the accepted answer, and I'm not specifying any status code. I'm also using the session state for parameters. The relevant code looks something like this:

public function origin(Request $request) {
  // Assume I have set variables $user and $cvId
  return redirect()
    ->action('SampleController@confirmUser')
    ->with([
      'cvId' => $cvId,
      'userId' => $user->id,
     ]);
}

public function confirmUser(Request $request) {
  $cvId = session()->get('cvId');
  $userId = session()->get('userId');

  if (is_null($cvId) || is_null($userId)) {
    // This is reached on the second time this is called, as 
    // the session variables aren't set the second time
    return redirect('/home');
  }

  // We only see the view for fractions of a second before we are redirected home
  return view('sample.confirmUser', compact('user', 'cvId'));
}

Any ideas what could be causing this? I don't have any next middleware or any of the other possible causes that are suggested in related questions where controllers are executed twice.

Thanks for any help!

via Chebli Mohamed