Inconsistent catch-all route behavior between local build & Vercel

Help
1

I’m seeing inconsistent routing behavior between visiting my local Next.js production build and my Vercel production deployment.

Setup

  • Next.js v15.2.3
  • Using pages router
  • Node v20.17.0

This is a simplified representation of the routes

pages/
├── [[...catchallslug]].tsx      <-- Top-level catch-all route. Requests external CMS
└── shop/
    └── shirts/
        └── [...slug].tsx       <-- Nested dynamic route for shirt product pages. These should be generated on buildtime

Route Configuration:

  • [...slug].tsx uses fallback: false with a hardcoded array of paths:
    • /shop/shirts/adidas/original-tee
    • /shop/shirts/adidas/performance-tee
  • [[...catchallslug]].tsx uses fallback: 'blocking' to handle unmatched routes

The Issue:

Local behavior (expected): When visiting /shop/shirts/adidas/something (a non-generated path), the request falls back to the top-level catch-all route [[...catchallslug]].tsx.

Vercel behavior (unexpected): The same URL triggers [...slug].tsx and runs its getStaticProps , despite fallback: false . I expect this to return a 404 since the path wasn’t pre-generated. Also, the response includes the header x-matched-path: /[[...catchallslug]] , indicating Vercel internally knows it should match the optional catch-all route, yet it still renders the [...slug].tsx template and executes its getStaticProps

Key observation: When I remove [[...catchallslug]].tsx entirely, Vercel correctly returns a 404 for /shop/shirts/adidas/something .

Why does the presence of a top-level optional catch-all route affect how Vercel handles fallback: false in nested routes? How can I maintain consistent behavior across environments?

Edit) This also seems to apply when using the App Router under a similar route setup

2

There’s another community post with 404 debugging tips that might be helpful. Please give these solutions a try and let us know how it goes.

A human should be around soon to offer more advice. But you can also get helpful information quickly by asking v0.