Disable Related Products?

Try this in functions.php. It will be overwritten by your next theme update. To avoid this recurring problem, make a child theme and put the code in functions.php for the child theme.

// remove related products
  remove_action('woocommerce_after_single_product_summary', 'woocommerce_output_related_products', 20);

Alternatively, allow them to generate but hide them with this in your custom css:

.related.products {display:none}

Isn’t this something that can be disabled by toggling a check box? Why is it randomly happening? Why does something not happen and then suddenly start happening? Why do I have to write code for something that shouldn’t be happening to begin with? Doesn’t this indicate some kind of malfunction that should be addressed rather than patching it, for better or worse?

I figured it out. I deselected the product category. Ridiculous.