Webforms are not redirecting to the custom "access denied" page

That's really weird!

I used the same configuration as yours but still the same problem!

On my test website, I have created a test webform: Record a transaction with access permission only to "administrator".
The alias of all my webform is: task

Now, as anonymous user (not logged in):
Visit: http://testdrupal.ml/task/record-a-transaction and you will see the default access denied page...
However, if you visit: http://testdrupal.ml/admin/structure/views, you will see a custom access denied page.

Below is my exported webform:

uuid: 266395ab-e760-40cf-96ba-8420e9082a5a
langcode: en
status: open
dependencies: {  }
open: null
close: null
weight: 0
uid: 1
template: false
archive: false
id: record_a_transaction
title: 'Record a transaction'
description: ''
category: ''
elements: |
  transaction_name:
    '#type': textfield
    '#title': 'Transaction Name'
    '#required': true
    '#multiple__no_items_message': '<p>No items entered. Please add items below.</p>'
css: ''
javascript: ''
settings:
  ajax: true
  ajax_scroll_top: form
  page: true
  page_submit_path: ''
  page_confirm_path: ''
  form_title: both
  form_submit_once: false
  form_exception_message: ''
  form_open_message: ''
  form_close_message: ''
  form_previous_submissions: false
  form_confidential: false
  form_confidential_message: ''
  form_remote_addr: true
  form_convert_anonymous: false
  form_prepopulate: false
  form_prepopulate_source_entity: true
  form_prepopulate_source_entity_required: false
  form_prepopulate_source_entity_type: ''
  form_reset: false
  form_disable_autocomplete: false
  form_novalidate: false
  form_disable_inline_errors: false
  form_required: false
  form_unsaved: false
  form_disable_back: false
  form_submit_back: false
  form_autofocus: false
  form_details_toggle: false
  form_access_denied: default
  form_access_denied_title: ''
  form_access_denied_message: ''
  form_access_denied_attributes: {  }
  form_file_limit: ''
  submission_label: ''
  submission_log: false
  submission_views: {  }
  submission_views_replace:
    webform_routes: {  }
    node_routes: {  }
  submission_user_columns: {  }
  submission_user_duplicate: false
  submission_access_denied: default
  submission_access_denied_title: ''
  submission_access_denied_message: ''
  submission_access_denied_attributes: {  }
  submission_exception_message: ''
  submission_locked_message: ''
  submission_excluded_elements: {  }
  submission_exclude_empty: false
  submission_exclude_empty_checkbox: false
  previous_submission_message: ''
  previous_submissions_message: ''
  autofill: false
  autofill_message: ''
  autofill_excluded_elements: {  }
  wizard_progress_bar: true
  wizard_progress_pages: false
  wizard_progress_percentage: false
  wizard_progress_link: false
  wizard_start_label: ''
  wizard_preview_link: false
  wizard_confirmation: true
  wizard_confirmation_label: ''
  wizard_track: ''
  preview: 0
  preview_label: ''
  preview_title: ''
  preview_message: ''
  preview_attributes: {  }
  preview_excluded_elements: {  }
  preview_exclude_empty: true
  preview_exclude_empty_checkbox: false
  draft: none
  draft_multiple: false
  draft_auto_save: false
  draft_saved_message: ''
  draft_loaded_message: ''
  confirmation_type: inline
  confirmation_title: ''
  confirmation_message: ''
  confirmation_url: ''
  confirmation_attributes:
    class:
      - 'messages messages--status'
  confirmation_back: false
  confirmation_back_label: ''
  confirmation_back_attributes: {  }
  confirmation_exclude_query: false
  confirmation_exclude_token: false
  limit_total: null
  limit_total_interval: null
  limit_total_message: ''
  limit_total_unique: false
  limit_user: null
  limit_user_interval: null
  limit_user_message: ''
  limit_user_unique: false
  entity_limit_total: null
  entity_limit_total_interval: null
  entity_limit_user: null
  entity_limit_user_interval: null
  purge: none
  purge_days: null
  results_disabled: false
  results_disabled_ignore: false
  token_update: false
access:
  create:
    roles:
      - administrator
    users: {  }
    permissions: {  }
  view_any:
    roles: {  }
    users: {  }
    permissions: {  }
  update_any:
    roles: {  }
    users: {  }
    permissions: {  }
  delete_any:
    roles: {  }
    users: {  }
    permissions: {  }
  purge_any:
    roles: {  }
    users: {  }
    permissions: {  }
  view_own:
    roles: {  }
    users: {  }
    permissions: {  }
  update_own:
    roles: {  }
    users: {  }
    permissions: {  }
  delete_own:
    roles: {  }
    users: {  }
    permissions: {  }
  administer:
    roles: {  }
    users: {  }
    permissions: {  }
  test:
    roles: {  }
    users: {  }
    permissions: {  }
  configuration:
    roles: {  }
    users: {  }
    permissions: {  }
handlers: {  }

Thank you,

I just updated the module to the latest dev release from 8.x-5.1 version... and now the issue is gone!

Thank you for your time and effort