Inconsistent page data in custom output format

[jamiebrynes7]

Description

I've noticed that some page data is missing when attempting to access it in a custom output format. I've only observed this issue when attempting to access a translated page's properties.

Given the following config:

baseURL = 'http://example.org/'
title = 'My New Hugo Site'

languageCode = "en"
defaultContentLanguage = "en"


[languages]
  [languages.en]
    title = "Repro"
    languageName = "English"
    contentDir = "content/en"
    weight = 1

  [languages.zh_CN]
    title = "Repro"
    weight = 2
    languageName = "简体中文"
    contentDir = "content/zh_CN"

[outputFormats]
  [outputFormats.metadata]
    baseName = "metadata"
    mediaType = "text/html"
    isPlainText = true
    notAlternative = true

[outputs]
    home = ["HTML", "metadata"]

... and the following templates:

home.html

<h2>Translations</h2>
<ul>
{{ range .Site.Menus.main }}
  {{ $p := .Page }}
  {{ range $p.Translations}}
    <li>{{ .Title }}, {{ .Summary }}</li>
  {{ end }}
{{ end }}
</ul>

metadata.home.html

<h2>Translations</h2>
<ul>
{{ range .Site.Menus.main }}
  {{ $p := .Page }}
  {{ range $p.Translations}}
    <li>{{ .Title }}, {{ .Summary }}</li>
  {{ end }}
{{ end }}
</ul>

will produce different results. In this case, only for the English generation of metadata.home.html, the .Summary property for the translated page is empty:

You can find a repro of this case in https://github.com/jamiebrynes7/hugo-repro-missing-data with the associated configuration and page data.

What version of Hugo are you using (hugo version)?

$ hugo version
hugo v0.87.0-B0C541E4+extended windows/amd64 BuildDate=2021-08-03T10:57:28Z VendorInfo=gohugoio

Does this issue reproduce with the latest release?

Yes

[jmooring]

I suspect that this behavior might be limited to the summary field, due to the unique way this field is handled. See my recent comments.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. The resources of the Hugo team are limited, and so we are asking for your help.
If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open.
If this is a feature request, and you feel that it is still relevant and valuable, please tell us why.
This issue will automatically be closed in the near future if no further activity occurs. Thank you for all your contributions.

[ptgott]

Replying to keep this issue open while I respond to the review of PR #9342

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.