The website encountered an unexpected error. Please try again later (WSOD). Debugging scenario
1- Install Drush if you have not installed it already.

2- Clear cache using drush.

3- Still if you are facing issues start debugging with error logs as following.

Add the following lines to your settings.php

error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);


While editing settings.php change its default file permission to writable. 
And you may also add following to your settings.php

$config['system.logging']['error_level'] = 'verbose';


Additional information is available here!

4- If you see any error related to any custom/contributed module after enabling error reporting service.You may overwrite the particular module folder with its latest release or even try with its dev release

5- You can read the server log messages for additional error informations. These log files may vary as per the server configurations. Some information about the server log file available here!