Do you have wp_debug on?
https://codex.wordpress.org/WP_DEBUG
If not please activate it and see if it turns up any notices/warnings/errors..
Here’s a snippet I like to place in my wo-config file which’ll save all issues to a debug.log file in wp-content rather than spit them out directly on the screen.
// Turns WordPress debugging on
define('WP_DEBUG', true);
// Tells WordPress to log everything to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);
// Doesn't force the PHP 'display_errors' variable to be on
define('WP_DEBUG_DISPLAY', false);
// Hides errors from being displayed on-screen
@ini_set('display_errors', 0);
