How to filter posts by category on archive / template page?

Hi all, I am trying to filter posts by category on a custom archive / template page. My template page currently has a custom query which displays posts from four specific categories. Then I have a select (dropdown) form, that in theory, filters the posts by a chosen one of the four categories.

<form id="category-select" class="category-select" action="<?php echo esc_url( home_url( '/business-ready/news-updates-new/' ) ); ?>" method="get">
<li>
		<?php
		$args = array(
			'show_option_none' => __( 'Category' ),
			'show_count'       => 0,
			'orderby'          => 'name',
			'echo'             => 0,
			'class'            => 'search-select',
		);
		?>
		<?php $select  = wp_dropdown_categories( $args ); ?>
		<?php echo $select; ?>
	</li>
	<li><input type="submit" value="GO!" /></li>
</form>

This select form works on the main blog archive page, but not my custom template page. Any ideas? Am I missing something? All and any help is appreciated, thanks in advance!