This is because the middleware StartSessionis inside $middlewareGroups(the middleware groups of the application), so you do not have access to the authenticated user, because the intermediaries that initialize your session start later in the life cycle than ExceptionHandler.
In the file, app\Kernel.phpmove this line:
\Illuminate\Session\Middleware\StartSession::class,
$middlewareGroups $middleware. , Auth::user() .
: cookie. file .
UPDATE:
StartSession $middleware, cookie session driver, $middlewareGroup $middleware :
\App\Http\Middleware\EncryptCookies::class,
\Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
\Illuminate\Session\Middleware\StartSession::class