InlineRepeater on custom field

[kfina-planxy]

In my ModelRepository I generate an array based on some fields/relations/etc.
Then in the ModelControllere I have an InlineRepeater based on that custom generated field.
The InlineRepeater is empty, although the array given with the same id is not empty.

ModelRepository.php

    use HandleJsonRepeaters;
    protected $jsonRepeaters = [ "myarray" ]; // I tried it both with and without this line

    public function getFormFields($object): array
    {
        $fields = parent::getFormFields($object);
        ... // code to fill my array, it's relatively long, so I'll spare the details. You can see the result from the dd below.
        dd($fields["myarray"]);
        return $fields;
    }

ModelController.php

    public function getForm(TwillModelContract $model): Form
    {
        $form = parent::getForm($model);
        ... // other fields

        $form->add( InlineRepeater::make()->name("myarray")->label("Prefabs")->fields([
            Input::make()->name("key")->label("Internal ID")->readOnly(),
            Input::make()->name("label")->label("Prefab Type")->readOnly(),
            Checkbox::make()->name("active")->label("Activated"),
        ]));
        return $form;
    }

All I get is an empty InlineRepeater.
I compared it with $fields from another InlineRepeater, and added the fields like ["medias" => [], etc. ], which doesn't help at all.
Why isn't this working? The data I provide is in exactly the same shape as the other working inline-repeater fields.

For Reference, this is how dd($fields["..."]) of a working InlineRepeater field looks like: