First of all, enable debugging in WordPress by setting this in your **wp-config.php** file:

    define( 'WP_DEBUG', true );

After that you could also increase the memory allocated to PHP by setting this in your **wp-config.php** file:

    define( 'WP_MAX_MEMORY_LIMIT', '256M' );

More information about editing the **wp-config.php** file / WordPress configuration file, see: https://codex.wordpress.org/Editing_wp-config.php

For more information about debugging see below and/or this link: https://codex.wordpress.org/Debugging_in_WordPress

> Example wp-config.php for Debugging
> -----------------------------------
> 
> The following code, inserted in your wp-config.php file, will log all
> errors, notices, and warnings to a file called debug.log in the
> wp-content directory. It will also display the errors.
> 
>     // Enable WP_DEBUG mode
>     define( 'WP_DEBUG', true );
>     
>     // Enable Debug logging to the /wp-content/debug.log file
>     define( 'WP_DEBUG_LOG', true );
>     
>     // The SAVEQUERIES definition saves the database queries to an array and that array can be displayed to help analyze those queries.  
>     define( 'SAVEQUERIES', true );