Why are my entries disappearing when {% if category | length %} is added? Editing an index page that displays all entries within a structure. 

Everything displays fine. 

I add a category to a few entries and add {% if category | length %}and everything disappears as if no entries had a category. 

I get no twig errors, so I presume my code is okay.

Here it is, just in case:

          {% set entries = craft.entries.section('fellows').relatedTo(category) %}
      {% if category | length %}
        {% if entries | length %}
          {% for entry in entries %}
            {% for matrixBlock in entry.fellowsEntry %}
              {% if matrixBlock.type == 'entryContent' %}

                &lt;a href="{{ entry.url }}" class="portfolio-view bio"&gt; 
                    &lt;div class="portfolio-index inner bio m-white col-md-12"&gt;
                        {% for image in matrixBlock.fellowImage %} 
                           &lt;img src="{{ image.getUrl('sq300x300') }} " alt="" class="image-portfolio"&gt;
                         {% endfor %} 
                        &lt;h3 class="name text-center p22-ltp"&gt;{{ entry.title }}&lt;/h3&gt;
                        &lt;hr&gt;
                        &lt;h3 class="org text-center p22-ltp"&gt;{{ matrixBlock.organization }} &lt;/h3&gt;
                        &lt;hr&gt;
                        {{ category }}
                    &lt;/div&gt;&lt;/a&gt; 

             {% endif %}
          {% endfor %} 
        {% endfor %}   
      {% endif %}
    {% endif %}
My Category URL Formats was set-up incorrectly. Or rather, I needed to go to {handle}/{slug} to see the proper result.