Cache and Pagination not working
Based on the code you posted on pastebin, it seems like the problem is that you have your pagination outside of the cache tags (assuming this was the case when you had caching implemented). And, I'm assuming that inside your {% include "_includes/pagination" %} you're trying to access pageInfo, which is created by the pagination tag. 

To make this work, and be able to implement efficient caching, you need to include your pagination inside your cache tags. In fact, I would also include the logic that creates the topicEntries element criteria above where you have the pagination tag today, inside the cache tag, as it creates DB queries and is directly related to the content you want to cache. 

The overall structure of your code should then be:

{% cache globally using key craft.request.path ~ '/p' ~ craft.request.getPageNum for 2 hours %}
    &lt;ul class="feat-box-container"&gt;
        {#  lots of code to get topicEntries #}

        {% paginate topicEntries.limit(10) as pageInfo, topicEntries %}

        {% for topic in topicEntries %}
            {# code that outputs list items #}
        {% endfor %}
    &lt;/ul&gt;

    {% include "_includes/pagination" %}
{% endcache %}