Let's not fool ourselves here guys. The accepted answer only got the user to his goal.
The very first problem lies here:
<?php
// display upsells and related products within dedicated div with different column and number of products
remove_action( 'woocommerce_after_single_product_summary', 'woocommerce_output_related_products',20);
remove_action( 'woocommerce_after_single_product', 'woocommerce_output_related_products',10);
add_action( 'woocommerce_after_single_product_summary', 'woocommerce_output_related_products', 20);
An action is removed, and then placed in the EXACT position it was removed from. The goal is completely unclear.
I came across this with a search on the related products because I did not understand that TAGS and CATEGORIES are what drives the woocommerce_output_related_products
function in this plugin.
The best answer to THIS question is the following link, and has everything to do with the woocommerce_output_related_products_args()
filter: http://stackoverflow.com/questions/23554993/output-posts-relating-to-the-tagshttps://stackoverflow.com/questions/23554993/output-posts-relating-to-the-tags