We are using WP Engine for our WordPress websites and we have started working on migrating our sites from PHP 5.6 to PHP 7.2 since November 2018.
Recently, after making all migration fixes, when we moved our website to WP Engine staging setup in PHP 7.2 environment, we started seeing below warning which was not coming in our local developer setup.
Warning: Parameter 1 to wp_default_scripts() expected to be a reference, value given in /<my_site_path>/wp-includes/class-wp-hook.php on line 286
I tried all way like turned off all plugins, changed theme etc but we were not able to trace this issue. Later, I setup the same install in my other server and everything started working properly. Hence, I come to know that this must be an issue with WP Engine.
I checked with them with all evidence and at last, they confirmed that there is some issue with their PHP 7.2 setup and they will look it and update. I doubt they will fix it very soon but till that time you can ignore this error.