Try to add the following PHP code snippet to the child theme functions.php file to fix this

function basel_category_thumb_double_size( $category ) {
	global $basel_loop;
	$small_thumbnail_size  	= apply_filters( 'subcategory_archive_thumbnail_size', 'woocommerce_thumbnail' );
	$dimensions    			= wc_get_image_size( $small_thumbnail_size );
	$thumbnail_id  			= get_woocommerce_term_meta( $category->term_id, 'thumbnail_id', true  );
        $attr_height 			= '';

	if( ! empty( $basel_loop['double_size'] ) && $basel_loop['double_size'] ) {
		$small_thumbnail_size = 'shop_catalog_x2';
		$dimensions['width'] *= 2;
		if ( $dimensions['height'] ) {
			$dimensions['height'] *= 2;
			$attr_height = 'height="' . esc_attr( $dimensions['height'] ) . '"';
		}
	}

	if ( $thumbnail_id ) {
		$image = wp_get_attachment_image_src( $thumbnail_id, $small_thumbnail_size  );
		$image = $image[0];
	} else {
		$image = wc_placeholder_img_src();
	}

	if ( $image ) {
		// Prevent esc_url from breaking spaces in urls for image embeds
		// Ref: https://core.trac.wordpress.org/ticket/23605
		$image = str_replace( ' ', '%20', $image );

		echo '<img src="' . esc_url( $image ) . '" alt="' . esc_attr( $category->name ) . '" width="' . esc_attr( $dimensions['width'] ) . '" ' . $attr_height . ' />';
	}
}