Part of admin template is ignored when deploying

[xtlc]

I already opened an unanswered post on ​Stackoverflow, which is the reason why I come here:

I changed the change_form.html and the submit_line.html template within one of my projects. The change_form.html now reads:

{% extends "admin/change_form.html" %}
{% load i18n admin_urls %}


{% block after_field_sets %}
    <h3>Preview (reload page for actual preview):</h3><br />
    {{ img }}    
{% endblock %}

{% block inline_field_sets %}
    {% for inline_admin_formset in inline_admin_formsets %}
        {% include inline_admin_formset.opts.template %}
    {% endfor %}
    warning!
{% endblock %}

and the submit_line.html:

{% load i18n admin_urls %}
<div class="submit-row">
    {% if show_save %}<input type="submit" value="{% trans 'Save' %}" class="default" name="_save" />{% endif %}
    {% if show_delete_link %}
        {% url opts|admin_urlname:'delete' original.pk|admin_urlquote as delete_url %}
        <p class="deletelink-box"><a href="{% add_preserved_filters delete_url %}" class="deletelink">{% trans "Delete" %}</a></p>
    {% endif %}
    {% if show_download_zip %}
        <input type="submit" value="zip" name="_download_zip" />
    {% endif %}
    {% if show_save_as_new %}
        <input type="submit" value="{% trans 'Save as new' %}" name="_saveasnew" />
    {% endif %}
    {% if show_save_and_add_another %}
        <input type="submit" value="{% trans 'Save and add another' %}" name="_addanother" />
    {% endif %}
    {% if show_save_and_continue %}
        <input type="submit" value="{% trans 'Save and continue editing' %}" name="_continue" />
    {% endif %}
</div>

In my corresponding admin class I added:

    def render_change_form(self, request, context, *args, **kwargs):
        if not context["original"] == None:
            context.update({'show_download_CSV': True})
        return super().render_change_form(request, context, *args, **kwargs)

and now for the part that is bugging me. When DEBUG = True is set, the result looks like this:

but when setting DEBUG= False:

I can not see any errors what so ever. I do not know if this is a bug or maybe just a silly mistake on my side, but any help on what could be checked is appreciated. This was tested on 3.2.8.