[Fixed]-NoReverseMatch when rendering page

Try using tuples:

View:

context['sections'] = [(section, tuple(get_subsections(section))) for section in sections]

Template:

{% for section, subsections in sections %}
    <a class="sections" href="{% url 'sections:generate' section.slug %}">{{ section.title }}</a>
    {% for subsection in subsections %}
        <p>{{ subsection.title }}</p>
    {% endfor %}
{% endfor %}