When a model cannot be found, the following 404 page is shown:

In order to debug which model, edit app/Exceptions/Handler.php:

public function render($request, Throwable $e) {
    if ($e instanceof  ModelNotFoundException && Config::get('app.debug') === true) {
        return response()->json(['error' => $e->getMessage()]);
    }
    return parent::render($request, $e);
}