Page with a dynamic route can receive an incorrect params when deployed to Vercel

[ferrata]

Link to the code that reproduces this issue

https://github.com/ferrata/nextjs-dynamic

To Reproduce

1. Go to the test page
2. The page shows params that were passed, and they are different from the expected:

Current vs. Expected behavior

The page should receive correct params:

{
  "locale": "en",
  "rest": [
    "folder",
    "page"
  ]
}

But instead receives incorrect params:

{
  "locale": "folder",
  "rest": [
    "page"
  ]
}

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.3.0: Thu Jan  2 20:24:16 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 18.20.2
  npm: 10.5.0
  Yarn: N/A
  pnpm: 9.15.4
Relevant Packages:
  next: 15.3.0-canary.31 // Latest available version is detected (15.3.0-canary.31).
  eslint-config-next: 15.2.4
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Dynamic Routes

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

Under certain conditions, for a page with dynamic route an incorrect params are passed to the page

The error is reproducing for me when the following conditions are met:

• the page in question has a dynamic route
• the parent route of the dynamic route has PPR (Partial Prerendering) enabled
• a middleware is used to rewrite an original URL to patch a route (prepend a locale in my case)
• the project is deployed on Vercel

Important

Note 1: The issue is not reproducible locally.

Important

Note 2: The parameters are passed correctly when navigating to the page from another route. The issue reproduces only when the page is loaded directly, or by refreshing the page.