[4.x]: /admin wrong password results in undefined error

What happened?

Description

So on a site if you try to login into the cms and you enter a faulty password you get the undefined error:

We do have a custom login url here instead of /admin however changing this has no effect.
Our general.php looks like this:
return GeneralConfig::create() ->limitAutoSlugsToAscii() ->convertFilenamesToAscii() ->enableGql(false) // Prevent generated URLs from including "index.php" ->omitScriptNameInUrls() ->useEmailAsUsername() // Set the default week start day for date pickers (0 = Sunday, 1 = Monday, etc.) ->defaultWeekStartDay(1) // Enable Dev Mode ->devMode(App::env('DEV_MODE') ?? false) // Allow administrative changes ->allowAdminChanges(App::env('ALLOW_ADMIN_CHANGES') ?? false) // Allow updates ->allowUpdates(App::env('ALLOW_UPDATES') ?? false) ->userSessionDuration(7200) // Disallow robots ->disallowRobots(App::env('DISALLOW_ROBOTS') ?? true) ->cpTrigger('prodelta-admin') ->aliases([ '@assetBaseUrl' => getenv('ASSET_BASE_URL'), '@assetBasePath' => getenv('ASSET_BASE_PATH'), '@baseUrl' => getenv('PRIMARY_SITE_URL'), '@web' => getenv('PRIMARY_SITE_URL'), '@basePath' => getenv('BASE_PATH'), '@systemEmail' => getenv('SYSTEM_EMAIL'), '@recaptchaKey' => getenv('RECAPTCHA_KEY'), '@recaptchaSecretKey' => getenv('RECAPTCHA_SECRET_KEY'), '@gtagKey' => getenv('GTAG_KEY'), '@lazyloadPlaceholder'=> "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7", ]);

Steps to reproduce

1. Enter a wrong password in /admin (I'm guessing this is a server issue, in the requirements overview everything is checked)

Expected behavior

Return the error that either the username or password is invalid

Actual behavior

Returning an undefined error.

Craft CMS version

4.5.6.1

PHP version

8.1.22

Operating system and version

No response

Database type and version

mysqlnd 8.1.22

Image driver and version

No response

Installed plugins and versions

Start by reproducing the wrong-password login at the configured custom admin trigger, prodelta-admin, using Craft CMS 4.5.6.1 and PHP 8.1.22, then trace where the undefined error is produced. Done means invalid credentials consistently return a clear username-or-password error instead of an undefined error.