Pages router with middleware (on vercel) - 404 results returning 200 when prefetched

[magicspon]

Link to the code that reproduces this issue

https://github.com/magicspon/next-link-test

To Reproduce

Build and deploy the app to vercel.
Go to the URL
Click on the "Broken link" button.
Observe, the 404 page is not shown.

This only happens when running on vercel, it's fine on localhost.

It also only happens when there is middleware on the site, even though these urls aren't matched by the middleware

Current vs. Expected behavior

When clicking on a link that 404's, I would expect to see the 404 page.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.6.0: Mon Jul 29 21:13:04 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6020
  Available memory (MB): 16384
  Available CPU cores: 12
Binaries:
  Node: 20.17.0
  npm: 10.8.2
  Yarn: 1.22.19
  pnpm: 8.14.0
Relevant Packages:
  next: 15.0.4-canary.11 // Latest available version is detected (15.0.4-canary.11).
  eslint-config-next: 15.0.3
  react: 19.0.0-rc-7ac8e612-20241113
  react-dom: 19.0.0-rc-7ac8e612-20241113
  typescript: 5.6.3
Next.js Config:
  output: N/A

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

create-next-app, Middleware, Pages Router

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

Vercel (Deployed)

Additional context

I've tested against the latest v14 release, the latest 15 release and the latest 15 canary release.

#57207
#56222