by Usman Asar.
Eugene, one possible error (as I encountered it as when I copied over php.ini from PHP 5.x to PHP 7.x) was due to mysql extension, looking into error log it was showing "couldn't load MySQL extension" as if you see php extension_mysql was present in v 5.x, but is missing from 7.x, so I disabled it in php.ini of PHP 7.x, only available extension in php 7.x is mysqli, after that I stopped getting 500 errors.