on is_mobile_cpcss_active() {
		return (
			$this->options->get( 'async_css', 0 )
			&&
			$this->options->get( 'cache_mobile', 0 )
			&&
			$this->options->get( 'do_caching_mobile_files', 0 )
		)
		&&
		$this->options->get( 'async_css_mobile', 0 );
	}

	/**
	 * Checks if we should async CSS
	 *
	 * @since 3.6.2.1
	 *
	 * @return boolean
	 */
	private function should_async_css() {
		if ( rocket_get_constant( 'DONOTROCKETOPTIMIZE' ) ) {
			return false;
		}

		if ( ! $this->options->get( 'async_css', 0 ) ) {
			return false;
		}

		return ! is_rocket_post_excluded_option( 'async_css' );
	}

	/**
	 * Stops the critical CSS generation.
	 *
	 * @since 3.10
	 *
	 * @return void
	 */
	public function stop_critical_css_generation() {

		$this->critical_css->stop_generation();
		delete_transient( 'rocket_critical_css_generation_process_running' );
		delete_transient( 'rocket_critical_css_generation_process_complete' );
	}

	/**
	 * Display a notice to pass from CPCSS to RUCSS.
	 *
	 * @return void
	 */
	public function switch_to_rucss_notice() {
		$boxes = get_user_meta( get_current_user_id(), 'rocket_boxes', true );

		if ( in_array( __FUNCTION__, (array) $boxes, true ) ) {
			return;
		}

		if ( ! $this->options->get( 'async_css', 0 ) ) {
			return;
		}

		if ( $this->user->is_license_expired() ) {
			return;
		}

		$screen = get_current_screen();

		if ( isset( $screen->id ) && 'settings_page_wprocket' !== $screen->id ) {
			return;
		}

		/**
		 * Filters the status of the RUCSS option.
		 *
		 * @param array $should_disable will return array with disable status and text.
		 */
		$rucss_status = apply_filters(
			'rocket_disable_rucss_setting',
			[
				'disable' => false,
				'text'    => '',
			]
		);

		if ( is_array( $rucss_status ) && key_exists( 'disable', $rucss_status ) && $rucss_status['disable'] ) {
			return;
		}

		rocket_notice_html(
			[
				'status'                 => 'wpr-warning',
				'dismissible'            => '',
				'dismiss_button'         => __FUNCTION__,
				'message'                => sprintf(
					// translators: %1$ = opening bold tag, %2$ = closing bold tag.
					__( 'We highly recommend the %1$supdated Remove Unused CSS%2$s for a better CSS optimization. Load CSS Asynchronously is always available as a back-up.', 'rocket' ),
					'<b>',
							'</b>'
				),
				'action'                 => 'switch_to_rucss',
				'dismiss_button_message' => __( 'Stay with the old option', 'rocket' ),
			]
		);
	}

	/**
	 * Switch to RUCSS.
	 *
	 * @return void
	 */
	public function switch_to_rucss() {
		check_admin_referer( 'rucss_switch' );

		if ( ! current_user_can( 'rocket_manage_options' ) ) {
			wp_safe_redirect( wp_get_referer() );
			rocket_get_constant( 'WP_ROCKET_IS_TESTING', false ) ? wp_die() : exit;
			return; // phpcs:ignore Squiz.PHP.NonExecutableCode.Unreachable
		}

		$this->options->set( 'async_css', false );
		$this->options->set( 'remove_unused_css', true );
		$this->options_api->set( 'settings', $this->options->get_options() );

		rocket_dismiss_box( 'switch_to_rucss_notice' );

		wp_safe_redirect( wp_get_referer() );
		rocket_get_constant( 'WP_ROCKET_IS_TESTING', false ) ? wp_die() : exit;
	}
}
<br />
<b>Fatal error</b>:  Uncaught TypeError: Argument 1 passed to WP_Rocket\Event_Management\Event_Manager::add_subscriber() must implement interface WP_Rocket\Event_Management\Subscriber_Interface, string given, called in /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/Plugin.php on line 155 and defined in /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/classes/event-management/class-event-manager.php:33
Stack trace:
#0 /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/Plugin.php(155): WP_Rocket\Event_Management\Event_Manager-&gt;add_subscriber('WP_Rocket\\Engin...')
#1 /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/main.php(42): WP_Rocket\Plugin-&gt;load()
#2 /home/merciket/public_html/wp-includes/class-wp-hook.php(324): rocket_init('')
#3 /home/merciket/public_html/wp-includes/class-wp-hook.php(348): WP_Hook-&gt;apply_filters(NULL, Array)
#4 /home/merciket/public_html/wp-includes/plugin.php(517): WP_Hook-&gt;do_action(Array)
#5 /home/merciket/public_html/wp-settings.php(506): do_action('plugins_l in <b>/home/merciket/public_html/wp-content/plugins/wp-rocket/inc/classes/event-management/class-event-manager.php</b> on line <b>33</b><br />