White Screen or 404 and Blank Site after Cloning

Symptoms after Cloning:

White Screen of Death
404 Page not Found
New cloned site exists but is empty or blank
Server Error 500

Applies to:

Multisite network installations running in Subdomain mode
Multisite network installations running in Subdirectory mode (also called Subfolder mode)

Cause and Solutions:

These symptoms almost always mean that the Cloner is unable to complete it's cloning process due inadequate system resource configurations.

The Cloner was originally designed as a site template cloning tool to save multisite admins a lot of time when deploying new copies of empty sites as a starting point for new sites. In order to use it for copying large, established sites with lots of plugins, posts, files, etc. your server performance settings will have to be tweaked to make sure that the Cloning process can complete.

The primary PHP settings that you should pay close attention to, and our recommended starting points for their settings are:

max_execution_time = 600 [this is in seconds]
memory_limit = 512MB

Some other things that you can do to ensure it has the best chances of completing successfully:

Make a DB backup before optimizing your database in case you need to go back or recover anything.
Delete and purge all post revisions and auto saves - your DB might have many times the number of posts in actual size from the revisions.
Delete and purge all transients
Make sure that “Capture additional debug logging to Detailed Log” option is NOT checked
Remove all unused plugins (and any tables they have created)
Purge all temporary data from active plugins (things like redirection logs, old activity logs, etc.)
Optimize the DB (There are several plugins that make this really simple)
Keep increasing max_execution_time and memory_limit as required. We've had to bump memory_limit as high as 768MB before to get some intense multisite plugins to work correctly.

When cloning large sites (anything above a couple hundred posts) with lots of plugins and files it is critical to make sure that all server resource limits are set adequately (memory and execution time) and that the DB itself has no unnecessary or extra data clutter.

Hopefully with every precaution taken you'll be able to clone even your larger sites!