Added Fields not rendered

Looking for some additional help. if I use a theme such as bartik, I can add and see extra fields like you'd expect. But with our custom theme, even with all .theme preprocess hooks disabled, all I can get displayed is the actual menu items. There doesn't seem to be any CSS hiding anything, as the HTML just doesn't have anything in it. Example my theme:

 <ul class="primary-nav usa-accordion" role="navigation" aria-label="Primary">
    
            <li class=" has-submenu ">

            
                <a class="accordion-button nav-link" aria-expanded="false" tabindex="0" aria-controls="megamenu-1">
                    <span>
                        Link of Level One
                        <span class="nav-arrow"></span>
                    </span>
                </a>
                  
  
            <ul id="megamenu-1" class="nav-submenu">

        
    
            <li class="">

                                                <a href="http://example.com" >
                                        <span>Link of Level Two</span>
                    </a>
                                    </li>
        </ul>
  

Example bartik:

<ul class="menu menu-level-0">
  
    <li class="menu-item menu-item--expanded">
      <a href="http://example.com" title="Sample Description">Link of Level One</a>


<div class="menu-item-teaser">
  <h2>Link of Level One</h2>
  

            <div class="field field--name-field-image field--type-image field--label-hidden field__item">

<img src="/sites/default/files/2020-10/test_iamge.jpg" width="583" height="524" alt="" typeof="foaf:Image" />

</div>
      


            <div class="clearfix text-formatted field field--name-field-body field--type-text-long field--label-hidden field__item"><p>Link of Level One Body Value</p></div>
      
<!-- END OUTPUT from 'core/themes/bartik/templates/classy/field/field--text-long.html.twig' -->


  <a href="http://example.com">Go to Link of Level One</a>
</div>

</ul>

The img tag in the second example is one of the extra fields. What could be stopping the module from actually generating and populating variables for the theme to display? The Demo seems to work fine in bartik, terms, images, body fields all show up. None of these do in our custom theme.

As a further followup. If I place some HTML comments into menu-link-content.html.twig and menu-levels.html in the contrib templates directory, I see those comments on Bartik, but none of the comments in my custom theme. It seems the twig isn't getting loaded in the custom, but I can't track down why that would be. Any ideas, appreciated.

Unfortunately, no. We had to find another module to replicate what we wanted to do with this module.