Puzzling Error

I've upgraded CodeIgniter from 3.9 to 4.2.1. I'm getting the following exception for all my routes except two. I don't understand why. I don't know what is different about the two that work. Invalid routes are not giving me same error and not Page Not Found page. I was using the legacy routing in the previous version.

ErrorException

preg_match(): Compilation failed: unmatched closing parenthesis at offset 23
SYSTEMPATH/Router/Router.php at line 418

My route config:

PHP Code:

$routes->setDefaultNamespace('App\Controllers');
$routes->setDefaultController('ReadPdf');
$routes->setDefaultMethod('index');
$routes->setTranslateURIDashes(false);
$routes->set404Override();
// The Auto Routing (Legacy) is very dangerous. It is easy to create vulnerable apps
// where controller filters or CSRF protection are bypassed.
// If you don't want to define all routes, please use the Auto Routing (Improved).
// Set `$autoRoutesImproved` to true in `app/Config/Feature.php` and set the following to true.
//$routes->setAutoRoute(false);

/*
 * --------------------------------------------------------------------
 * Route Definitions
 * --------------------------------------------------------------------
 */

// We get a performance increase by specifying the default
// route since we don't have to scan directories.
$routes->get('/', 'ReadPdf::index'); //does not work
$routes->get('/enroll', 'Enroll::index'); //works!
$routes->get('/notice', 'Notice::index'); //works!
$routes->get('/notice/upload', 'Notice::upload'); //?
$routes->get('/notice/download/{:segment)/(:segment)', 'Notice::download/$1/$2'); //?
$routes->get('/receive-pdf', 'ReceivePdf::index'); //all of these below don't work
$routes->get('/read-pdf', 'ReadPdf::index');
$routes->get('/relay-pdf', 'RelayPdf::index');
$routes->get('/reset-pdf', 'ResetPdf::index');
$routes->get('/reset-pdf/list', 'ResetPdf::list');
$routes->get('/reset-pdf/move', 'ResetPdf::move');
$routes->get('/server-up', 'ServerUp::index');
$routes->get('/test', 'Test::index'); 


Simpler is always better

$routes->get('/notice/download/{:segment)/(:segment)', 'Notice::download/$1/$2'); //?

$routes->get('/notice/download/{egment)/(egment)', 'Notice::download/$1/$2'); //?

Duh. Thanks.

Simpler is always better