White or Blank Screen when WP Rocket is Active

There are a few possible reasons why you may see a white or blank screen after activating WP Rocket. Here are some troubleshooting tips.

1.
 Check the error logs
A fatal PHP error is often hiding behind the blank screen so the first step to to is check your site's PHP error logs. If you don't know where to find them, ask your host. 

Or  enable WP_DEBUG.

2.
 Lack of PHP Memory
This will usually show up as a fatal error in the error log.
Please see this guide for an example of the error message and the solution.

3.
Misuse of output buffering functions
If you see this error in your log:
PHP Fatal error:  Call to a member function get() on null in /wp-includes/cache.php on line 123	

Check for this line in the functions.php of your theme:

remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );	

If you find, it comment it out, like this:

// remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );

When misused,  similar functions, for example, ob_get_clean and ob_end_clean can conflict with WP Rocket and cause fully or partially white screens.

4.
Conflict with another performance plugin
If you have another performance plugin with similar options, they can conflict. For example, some options in Clearfy-Pro cause a white screen.
5,
Deactivate File Optimization options
Try disabling all the options on the File Optimization tab in WP Rocket to see if the problem comes from a specific setting.