Events Calendar PRO: Remove Post Tags from the related posts logic and, therefore, only use Event Categories.

functions.php

<?php

/**
 * Events Calendar PRO: Remove Post Tags from the related posts logic and,
 * therefore, only use Event Categories. 
 * 
 * @see tribe_get_related_posts()
 *
 * @link https://gist.github.com/cliffordp/6a66affeab8ac57d7ceea942f8c417ff
 * 
 * @param $args
 *
 * @return array Multidimensional array that gets sent to Tribe__Events__Query::getEvents()
 */
function cliff_remove_tags_from_related_posts_logic( $args ) {
	if (
		! empty( $args['tax_query'][0]['taxonomy'] )
		&& 'post_tag' === $args['tax_query'][0]['taxonomy']
	) {
		if (
			! empty( $args['tax_query']['relation'] )
			&& 3 === count( $args['tax_query'] )
		) {
			unset( $args['tax_query']['relation'] );
		}

		unset( $args['tax_query'][0] );
	}

	return $args;
}

add_filter( 'tribe_related_posts_args', 'cliff_remove_tags_from_related_posts_logic' );