The message for class “Exception” causes PHP Fatal Error

That would be because inet_pton() is not meant to ouput strings, but bytes in network order (I don't remember if it's little endian or big endian).

Exception messages are not meant to include bytes, but printable characters. You can, however, put pure bytes into strings. These are then decoded to (probably) UTF-8 or other encoding to display readable text.

The following code

$message = inet_pton('119.252.33.171');
var_dump($message);
for($i = 0; $i < strlen($message); $i++)
{
   echo ord($message[$i]) . "\n";
}

Produces

string(4) "w�!�"
119
252
33
171

Compare these two lines

throw new \Exception(chr(33)); // Displays stacktrace
throw new \Exception(chr(252)); // Fails to output

My guess would be that an error occurs while PHP is trying to format the string as UTF-8 to print the exception message to stdout, but invalid UTF-8 string is passed in and the write/decoding fails.

Either way, seems like a bug in PHP.