Adding proxy causes requests to _next/data which return empty data

Link to the code that reproduces this issue

https://github.com/ari-party/repro-next-data-empty-object

To Reproduce

1. Clone this repo
2. npm install
3. npm run build
4. npm start
5. Go to http://localhost:3000
6. Open DevTools
7. Go to the network tab
8. Notice each additional _next/data request for each link to a page
9. Open any of the requests
10. View the response tab
11. Empty JSON response {}

Current vs. Expected behavior

Current: Requests made to _next/data/*/*.json
Expected: No requests made to _next/data/*/*.json
These empty data files bring no value and may cause a client error if the app is rebuilt, even if assetPrefix with hash is used.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #35~22.04.1-Ubuntu SMP Mon May 26 18:08:30 UTC 2025
  Available memory (MB): 7944
  Available CPU cores: 2
Binaries:
  Node: 24.11.1
  npm: 11.6.2
  Yarn: 1.22.22
  pnpm: 10.23.0
Relevant Packages:
  next: 16.1.6 // Latest available version is detected (16.1.6).
  eslint-config-next: 13.5.6
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

Middleware, Pages Router

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

next start (local)

Additional context

This a recreation of an older issue https://github.com/vercel/next.js/issues/59295.
This issue is present for both the deprecated middleware and the newer proxy.

Additionally might be related: https://github.com/vercel/next.js/issues/59612

Start with the linked reproduction: run npm install, npm run build, npm start, then inspect the middleware or proxy behavior for the Pages Router. Use the browser network tab to trace _next/data requests; done means the additional requests are no longer made and the existing reproduction still works.