Webform twig template causes "the form has become outdated" error
The issue was I was not rendering out the {{ element.form_token }} element. I added that element and it works:

{{ element.elements.form_description }}

&lt;form{{ attributes }}&gt;

{{ title_prefix }}

  {{ element.elements.my_element_01 }}
  {{ element.elements.my_element_02 }}

  {{ element.form_build_id }}
  {{ element.form_id }}
  {{ element.form_token }}
  {{ element.actions }}

{{ title_suffix }}

&lt;/form&gt;


This works which is why I submitted it as an answer. I do think it could be better written. This would require effectively using the twig 'without' filter which I can't get to work. I am creating a separate post about that as I feel they are different topics. The basic idea is I shouldn't have to fish or remember to render all the items that make up a drupal form such as form_build_id, form_id, form_token, or actions. I should render the entire element array and hide the fields I want to wrap in markup. Then I can explicitly render those fields. Something like:

{{ element.elements.form_description }}

&lt;form{{ attributes }}&gt;

{{ title_prefix }}

  {{ element|without('elements) }}

  {{ element.elements.my_element_01 }}
  {{ element.elements.my_element_02 }}

{{ title_suffix }}

&lt;/form&gt;


But that currently renders my_element_01 and my_element_02 twice.