Property does not exists in template although its assigned

I’m working on a Symfony application to add meter values to a meter. A meter can have a set of measurements, and for each measurement I want to display a value form to enter values.

Fot this I have a function in a controller that creates an ArrayCollection of empty (new) elements depending on the corresponding measurements like so:

/**
 * @Route("/{id}/add", name="metervalue_add", methods={"GET","POST"})
 */
public function add(Request $request, Meter $meter): Response
{
    $metervalues = new ArrayCollection();
    $measurements = $meter->getMeasurements();
    // create an empty metervalue for each measurement of the meter
    foreach ($measurements as $measurement) {
        $mv = new MeterValue();
        $mv->setMeter($meter);
        $mv->setMeasurement($measurement);
        $metervalues->add($mv);
    }
    $form = $this->createForm(MeterValueAddType::class, ['metervalues' => $metervalues]);

    $form->handleRequest($request);

    // ... form submitting stuff
    // ...

    return $this->renderForm('metervalue/add.html.twig', [
        'form' => $form
    ]);
}

The corresponding MeterValueAddType looks like

class MeterValueAddType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('metervalues', CollectionType::class, [
                'entry_type' => MeterValueType::class
            ]);
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'data_class' => null,
        ]);
    }
}

When I render the form all works fine, the empty objects are rendered as expected, I can submit the form and all data is inserted correctly in the DB, including measurement and meter ids.
However, in my template I cannot access reference properties of the metervalue object, like metervalues.measurement or metervalue.meter

{% for metervalue in form.metervalues %}
   {{ form_widget(metervalue.value) }}
   {{ form_widget(metervalue.date) }}

   Name of measurement: {{ metervalue.measurement.name }} <-- this throws the following error
{% endfor %}

Error: Neither the property “measurement” nor one of the methods
“measurement()”,
“getmeasurement()”/”ismeasurement()”/”hasmeasurement()” or “__call()”
exist and have public access in class
“SymfonyComponentFormFormView”.

I don’t understand why I can’t access the properties in here just to display them, as they are assigned above in the controller and stored correctly in the DB on save…

The property “measurement” and a correspoding “getmeasurement()” exist and e.g. if I display all saved objects in a list I can access these.

Any hints appreciated!