webP images in SilverStripe

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: 4.5.2

Question:

I have added webp images as a supported Image file type by SilverStripe.

Everything appears to works fine on the front end, Image Manipulation methods all seem to work. The only issue I have is thumbnails are not created in the asset manager in the CMS. Can anyone help me locate the code that looks after this. I am thinking it might be some javascript somewhere as the PHP code looks like it just uses FitMax which works fine on the front end.

## yml
SilverStripe\Assets\File:
  allowed_extensions:
    - webp
  app_categories:
    image/supported:
      - webp
  extensions:
    - Jellygnite\Extensions\FileExtension
SilverStripe\Assets\Storage\DBFile:
  supported_images:
    - image/webp
SilverStripe\Assets\Image:
  allowed_extensions:
    - webp


class FileExtension extends DataExtension {
    private static $class_for_file_extension = array(
        'webp' => Image::class
    );
}