How to fix broken sites after auto-updates has broken them.

The following is relevant 95% of the time when wordpress has done some auto-update process, and there was either not enough disc space on the account or some other erro casued the update to fail.
Look for a 0byte wp-config file in your file manager - Open it to edit it.

Navigate to : https://generatewp.com/wp-config/

Copy the contents of the file below on that page.

<?php
/**
 * Custom WordPress configurations on "wp-config.php" file.
 *
 * This file has the following configurations: MySQL settings, Table Prefix, Secret Keys, WordPress Language, ABSPATH and more.
 * For more information visit {@link https://codex.wordpress.org/Editing_wp-config.php Editing wp-config.php} Codex page.
 * Created using {@link http://generatewp.com/wp-config/ wp-config.php File Generator} on GenerateWP.com.
 *
 * @package WordPress
 * @generator GenerateWP.com
 *//* MySQL settings */
define('DB_NAME','database_name_here');
define('DB_USER','username_here');
define('DB_PASSWORD','password_here');
define('DB_HOST','localhost');
define('DB_CHARSET','utf8mb4');/* MySQL database table prefix. */
$table_prefix ='wp_';/* Authentication Unique Keys and Salts. *//* https://api.wordpress.org/secret-key/1.1/salt/ */
define('AUTH_KEY','put your unique phrase here');
define('SECURE_AUTH_KEY','put your unique phrase here');
define('LOGGED_IN_KEY','put your unique phrase here');
define('NONCE_KEY','put your unique phrase here');
define('AUTH_SALT','put your unique phrase here');
define('SECURE_AUTH_SALT','put your unique phrase here');
define('LOGGED_IN_SALT','put your unique phrase here');
define('NONCE_SALT','put your unique phrase here');/* Absolute path to the WordPress directory. */if(!defined('ABSPATH'))
	define('ABSPATH', dirname(__FILE__).'/');/* Sets up WordPress vars and included files. */
require_once(ABSPATH .'wp-settings.php');

Paste it into the opened wp-config.php you opened for editing earlier.
Get the details for :

define('DB_NAME','database_name_here');
define('DB_USER','username_here');
define('DB_PASSWORD','password_here');

From the wordpress installation page in cpanel, or in the mysql databases section and replace it as in the wp-config file.

$table_prefix = 'wp_';

From your wordpress database,

Save the file and close it, this should resolve the issue.