in your wp-config.php you will find a line that reads (most likely) like this:

define('WP_DEBUG', false);

REPLACE this with

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);/*this should NEVER be true for production sites*/

which will generate a file “wp-content/debug.log” if and when any errors are encountered. check this file for errors if you need to find out where things might go wrong