@Snapey You're right. I don't have any cookies. I thought I have... but this where from another app with the same local development domain.
But still no idea why.
My middleware groups:
protected $middlewareGroups = [
'web' => [
// MyMiddleware::class,
\App\Http\Middleware\EncryptCookies::class,
\Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
\Illuminate\Session\Middleware\StartSession::class,
// \Illuminate\Session\Middleware\AuthenticateSession::class,
\Illuminate\View\Middleware\ShareErrorsFromSession::class,
\App\Http\Middleware\VerifyCsrfToken::class,
\Illuminate\Routing\Middleware\SubstituteBindings::class,
],
'api' => [
// \Laravel\Sanctum\Http\Middleware\EnsureFrontendRequestsAreStateful::class,
'throttle:api',
\Illuminate\Routing\Middleware\SubstituteBindings::class,
],
];
The \Illuminate\Session\Middleware\AuthenticateSession::class looks suspicious. But was default off and is the same in all my other apps.
And tried it in a private browser (so no plugins which could cause this).