<div class="related-content padding">

  <div class="margin-bottom">
    <h2 class="inline-block">
      <%= t("related_content.title") %>&nbsp;<span>(<%= relationable.relationed_contents.count %>)</span>
    </h2>
    <% if current_user %>
      <button type="button" data-toggle="related_content" class="add-related-content" id="add-related-content">
        <%= t("related_content.add") %>
      </button>
    <% end %>
  </div>

  <% if current_user %>
    <%= render "relationable/form", relationable: relationable %>
  <% end %>

  <% if @related_contents.present? %>
    <%= render "relationable/related_list", relationable: relationable %>
  <% end %>

</div>

<div class="related-content padding">

  <div class="margin-bottom">
    <h2 class="inline-block">
      <%= t("related_content.title") %>&nbsp;<span>(<%= relationable.relationed_contents.count %>)</span>
    </h2>
    <% if current_user %>
      <button type="button" data-toggle="related_content" class="add-related-content">
        <%= t("related_content.add") %>
      </button>
    <% end %>
  </div>

  <% if current_user %>
    <%= render "relationable/form", relationable: relationable %>
  <% end %>

  <% if @related_contents.present? %>
    <%= render "relationable/related_list", relationable: relationable %>
  <% end %>

</div>

Remove unused related content button ID attribute
Remove unused related content button ID attribute
