I think there is something in your configuration that is avoiding showing Fatal errors on the screen.
For example, if you execute:
<?php x();
In this script, which actually calls a function that doesn't exist, you can see that no message is shown on the screen too. I saw that PHP is exiting with status code 0377 which means that a fatal error was produced somewhere but I can't figure out where it is. This also is happening instantiating classes that doesn't exist. I assume your problem is related with something like this.
Also, I enabled display_errors = On and error_reporting = E_ALL but it doesn't show the error. I don't have enough information on how the VPS is set up to avoid showing any errors. Maybe you could contact the provider.