Pagination page not added to custom frontmatter collection #4326

Operating system

Microsoft Windows 10 Home

Eleventy

3.1.6

Describe the bug

1. I created a filter to return all pages with the custom front matter mainMenu: true:

    eleventyConfig.addCollection("menuPages", function (collectionApi) {
        return collectionApi.getAll().filter((item) => item.data.mainMenu);
    });

2. I created a page that iterates through a tag collection

---
mainMenu: true
linkName: Thoughts
pagination:
  data: collections.thoughts
  size: 10
  alias: pageItems
  reverse: true
---

where collections.thoughts references pages with tags: thoughts in front matter - an equivalent to blog posts.

3. Despite having mainMenu: true after build, the first page of Thoughts collection does not appear in the menuPages collection. Other pages using pagination do appear in the menuPages collection, but they all iterate over collections originating from global data json files.

Expected behaviour:
when a page meets the criteria to be included in a collection, it is added to said collection, regardless of the data source it uses.

Reproduction Source Code URL

https://github.com/AqueM/webpage

Screenshots

No response