Wordpress random 500 internal server error

Can you enable WP_DEBUG, to see if you can catch something there, as sometimes it is more useful than the server logs.

To do this, open

wp-config.php

located in the directory where WordPress is installed and then locate the line with the code

define('WP_DEBUG', false);

and change it to

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

Ref:
https://stackoverflow.com/questions/31208302/wordpress-random-500-internal-server-error