Not sure if this problem is a Webform issue or a Bootstrap Theme issue.
Installed a clean Drupal site on my localhost testing server using composer to see what is causing this issue.
Installed the latest Webform module using composer and followed the instructions to install the libraries using the page below:
Using composer to install libraries for the Webform module
I have attached the webform.webform.hidden_visible (1).yml file as requested in one of your excellent videos.
Sorry if this post is long, but I thought the more information you have the better you can deal with this issue.
Any additional information you may require, I will endeavor to reply asap.
Created a new Webform and copied in a section from a Webform that was causing the issue.
Viewed the form using the Bartik theme. Image below:

Clicked on the Heathrow button and the hidden terminal buttons element showed with Terminal One selected as the default.

Changed the theme to the Bootstrap theme using the Default scheme.
Cleared all caches, then viewed the form as below:

Clicked on the Heathrow button and the hidden terminal buttons element showed with the issue as below.

| Comment | File | Size | Author |
|---|---|---|---|
| #4 | 3057639-4.patch | 597 bytes | jrockowitz |
| webform.webform.hidden_visible (1).yml | 5.64 KB | taxicab221 | |
| bootstrap-2.png | 38.01 KB | taxicab221 | |
| bootstrap-1.png | 21.95 KB | taxicab221 | |
| bartik-2.png | 28.38 KB | taxicab221 |
Comments
Comment #2
jrockowitz commentedI am not able to reproduce this issue using the latest dev release of the Webform module and Bootstrap 8.x-3.19.
Are you able to reproduce this problem using https://simplytest.me?
BTW, the latest dev release includes #3053190: Make it possible to style radios as buttons without using jQueryUi
Comment #3
taxicab221 commentedInstalled Webform to the latest dev version
composer require 'drupal/webform:5.x-dev'on another clean Drupal site.The
undefined undefined undefined undefined undefinederror is now resolved.The issue with the Default hidden Buttons element is still there. Works on the Bartik theme but not the Bootstrap theme.
On selecting the Heathrow or Gatwick options using the Bootstrap theme, the hidden Buttons option list element appears, the default option is active but not themed as the Active Button.
At what stage does the
webform:5.x-devversion become the standard for thecomposer require drupal/webformcommand, or should I always install the latest dev version?This is such a great module and the work you and your team have done is nothing but Fantastic.
Comment #4
jrockowitz commentedI recommend using the latest pre-release version which is 8.x-5.3-beta3.
composer require 'drupal/webform:^5.3'orcomposer require 'drupal/webform:5.3-beta3'Please test the attached patch which should fix the hidden issue in Bootstrap.
Comment #5
taxicab221 commentedApplied the patch at #4 on my test install.
Both issues now resolved. Many thanks.
I will now update the webform module on my main testing site to the latest pre-release version and apply the patch.
Comment #7
jrockowitz commented