Not sure if this has anything to do with your blank screen, but getting the field values should look something like this
$field = $_POST['acf']['field_5578ce8f3ccf1'];
$field2 = $_POST['acf']['field_5578ce8f3ccf1'];
You need to use the field keys for your fields instead of the field names.
If you still get a blank screen turn on error reporting on the site so you can see why it’s dying.
define('WP_DEBUG', true);
define('WP_DEBUG_DISPLAY', true);