Can't get modular collection in another page

Hi there,
I’m trying to get modular subpages in an another page, but it’s not working, the array I get is empty…

Here’s the frontmatter of the page where I want to get the modular subpages :

title: 'page title'
template: custom
content:
    items: 
        '@page.modular': '/modular-page'

the twig in the template :

{% for p in page.collection %}
     <h2>{{ p.title }}</h2>
{% endfor %}

and the modular.md frontmatter :

title: Modular Page
onpage_menu: true
body_classes: ""

content:
    items: '@self.modular'
    order:
        by: default
        dir: asc
        custom:
            - _modular-section-1
            - _modular-section-2
            - _modular-section-3
            - _modular-section-4

Am I missing something ?

Related issue: https://github.com/getgrav/grav/pull/1178