The "White Screen of Death" (WSOD) is a common issue in WordPress that can occur due to various reasons. When it happens on a WordPress Multisite installation, it can be a bit more complex to troubleshoot. Here are steps you can take to address this issue:

1. Enable Debugging:

   In your wp-config.php file set WP_DEBUG to true:

   php

• define( 'WP_DEBUG', true ); define( 'WP_DEBUG_DISPLAY', false );

  This will display any PHP errors. Check if there are any error messages displayed on the screen.

• Check for Plugin Conflicts:

  Disable all plugins by renaming the plugins folder inside wp-content (e.g., to plugins-old). Then, enable them one by one to identify if a specific plugin is causing the issue.

• Check for Theme Issues:

  Switch to a default theme (like Twenty Twenty-One) to see if the issue is related to the theme. If the site loads, it indicates a problem with your theme.

• Check File Permissions:

  Ensure that the files and directories have correct permissions. Incorrect permissions can cause issues. Generally, folders should be set to 755, and files should be set to 644.

• Check Memory Limit:

  Multisite installations may require more memory. Increase the memory limit in your wp-config.php file:

  php
• define( 'WP_MEMORY_LIMIT', '256M' );

• Check .htaccess file:

  Make sure your .htaccess file is correctly configured for a Multisite installation. You can compare it with a fresh WordPress Multisite .htaccess file.

• Check wp-config.php:

  Ensure that your wp-config.php file is correctly set up for Multisite. It should have the following lines:

  php

7. define( 'MULTISITE', true ); define( 'SUBDOMAIN_INSTALL', false ); define( 'DOMAIN_CURRENT_SITE', 'yourdomain.com' ); define( 'PATH_CURRENT_SITE', '/' ); define( 'SITE_ID_CURRENT_SITE', 1 ); define( 'BLOG_ID_CURRENT_SITE', 1 );

   Adjust the above constants according to your setup.

8. Check for Database Issues:

   Sometimes, database corruption or misconfiguration can cause issues. Use a plugin  WP-DBManager to repair and optimize the database.

9. Check Server Logs:

   Look at your server's error logs. They might contain information about what's causing the issue.

10. Check for PHP Version Compatibility:

    Ensure that your server is running a compatible version of PHP for your WordPress and its plugins/themes.

11. Contact Hosting Provider:

    If none of the above steps work, consider reaching out to your hosting provider for assistance. They might be able to identify any server-specific issues.

Remember to take backups before making any major changes, especially if you're modifying core files or the database. This way, you can easily revert to a working state if something goes wrong.