Re-adding core menus and widgets panels back if removed via 'customizer_loaded_components' hook. Note rehooking the nav menus customize_register() method at a later priority.

class-project-customizer.php

<?php
	require_once( ABSPATH . WPINC . '/class-wp-customize-widgets.php' );
	$this->wp_customize->widgets = new WP_Customize_Widgets( $this->wp_customize );

	require_once( ABSPATH . WPINC . '/class-wp-customize-nav-menus.php' );
	$this->wp_customize->nav_menus = new WP_Customize_Nav_Menus( $this->wp_customize );

	// Restore setup for nav menus (normally hooked at priority 11).
	add_action( 'customize_register', array( $this->wp_customize->nav_menus, 'customize_register' ), 501 );

	return;