This is part which rendering happen on replace function
// If a local $bubbleable_metadata object was created, apply the metadata
// it collected to the renderer's currently active render context.
if (!$bubbleable_metadata_is_passed_in && $this->renderer
$build = ;
For the first part of the question I still have no clue, it might not be (only) the delta the problem as I could work around it using computed twig data, but the fact the attachment and the number field are inside the composite, what may create a looping error.
As for the second question, here what worked for me using the computed twig from webform:
With twig_tweak (for twig token filter, tested on 8.x-2.9) you can add a token based link to the user account menu in Drupal 8/9 (/admin/structure/menu/manage/account).
E.g. A menu link:
Also works with multiple tokens.
title: [current-user:name] and [current-user:created]