Fix a temp issue between EDD Tickets 3.8 and EDD 2.1.9. Please place in your theme's functions.php file (or another suitable location) but be sure to remove the leading <?php tag as appropriate.

workaround-edd-print-tickets.php

class Tribe_EDDTickets_Fix31092 {
	/**
	 * Override EDDTickets' own print_ticket_url() callback.
	 */
	public function __construct() {
		add_filter( 'edd_download_file_url_args', array( $this, 'print_ticket_url' ), 20 );
	}

	/**
	 * @param $item
	 * @return bool
	 */
	protected function is_print_ticket_item( $item )
	{
		static $download_files = array();

		if ( empty($download_files) )
			$download_files = edd_get_download_files( $item['download_id'] );

		foreach ( $download_files as $index => $download ) {
			if ( $item['file'] != $index ) continue;
			if ( TribeEDDTickets::TICKET_DOWNLOAD === $download['file'] ) return true;
			if ( TribeEDDTickets::LEGACY_TICKET_DOWNLOAD === $download['file'] ) return true;
		}

		return false;
	}

	/**
	 * Setup the print ticket URL so that a print view is rendered instead of a download file
	 *
	 * @param array $args
	 *
	 * @return array
	 */
	public function print_ticket_url( $args = array() )
	{
		// Determine if this is a ticket product
		if ( ! get_post_meta( $args['download_id'], TribeEDDTickets::$event_key, true ) ) {
			return $args;
		}

		// Interfere only with the tickets link (thus allowing additional files to be downloaded
		// as part of the purchase)
		if ( ! $this->is_print_ticket_item( $args ) ) {
			return $args;
		}

		$args = array(
			'edd_action'   => 'print_ticket',
			'ticket'       => $args['download_id'],
			'download_key' => $args['download_key']
		);

		return $args;
	}
}

new Tribe_EDDTickets_Fix31092;