TypeError: Cannot read properties of undefined (reading 'forEach') on Vercel with minimal config

[ximosa]

Body:

Hello, I'm experiencing a persistent issue with Decap CMS on Vercel.

The admin panel (/admin) shows a blank page and the console error collections.js:23 Uncaught TypeError:
Cannot read properties of undefined (reading 'forEach').

This happens even with a minimal config.yml file.

My config.yml is:

1 backend:
2   name: github
3   repo: webgae/astro-decap-cms-blog
4   branch: main
5 client_id: Ov23liCklzov2dSy8xKr # (If you re-add it for testing)
6 
7 collections:
8   - name: "blog"
9     label: "Blog Posts"

10 folder: "src/content/blog"
11 fields:
12 - {label: "Title", name: "title", widget: "string"}

I have already tried:

• Fixing config.yml syntax (indentation, format property).
• Removing media_library and pages collection.
• Removing client_id (the error persists even without it).
• Ensuring vercel.json is configured for /admin (tried multiple rewrite rules).
• Removing redirects from astro.config.mjs.
• Aggressive browser cache clear and server restarts.
• The issue only occurs on Vercel, it works locally.

My Vercel URL is: https://astro-decap-cms-blog.vercel.app/admin/
My Decap CMS version is https://unpkg.com/decap-cms@^3.0.0/dist/decap-cms.js.

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Espero que esto te ayude a obtener una solución de la comunidad.