As hinted in https://github.com/symfony/symfony/pull/39196, xdebug changes the behavior of PHP when the Exception::$message property is set to a stringable object.

The following script yields an empty output when run with xdebug enabled, and echoes 'Hello World' on PHP (all versions >=7.0).
See https://3v4l.org/RGM4p

<?php

class LazyException extends Exception
{
public function construct()
{
parent::construct();

    $this->message = new class() {
        public function __toString()
        {
            return 'World';
        }
    };
}

}

$e = new LazyException();

try {
throw $e;
} catch (\Exception $e) {
echo 'Hello ';
echo $e->getMessage();
echo "\n";
}
?>