Middleware causing data loss with with preview apis

[jaandrews]

Link to the code that reproduces this issue

https://codesandbox.io/p/sandbox/muddy-sunset-nqqdr9

To Reproduce

I wasn't able to reproduce the issue in the sandbox, but it shows a simplified version of what I'm doing.

1. Open a preview in a new window, since the nested preview window doesn't add the preview cookie somewhere it can read.
2. Click "Enter Preview Mode" link to enter preview mode.
3. Click "End Preview"

Current vs. Expected behavior

When the "End Preview" link is clicked it should turn off preview mode and redirect back to the page that was previewed (based on documentation here). Instead it throws an error in my local environment because the data object is undefined.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Home
  Available memory (MB): 32370
  Available CPU cores: 16
Binaries:
  Node: 20.10.0
  npm: 8.18.0
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.1.6 // There is a newer version (15.1.7) available, upgrade recommended! (I also tested this with 15.2.0-canary.64, but had the same results)
  eslint-config-next: 14.2.3
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.4.5
Next.js Config:
  output: standalone
 ⚠ There is a newer version (15.1.7) available, upgrade recommended!
   Please try the latest canary version (`npm install next@canary`) to confirm the issue still exists before creating a new issue.
   Read more - https://nextjs.org/docs/messages/opening-an-issue

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

Middleware

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

next dev (local), Vercel (Deployed)

Additional context

When I delete middleware.ts it works as expected, so it's definitely something about how the middleware functions that is causing it to fail. I did notice that the data was there at there when the getStaticProps retrieves the data after preview mode is exited. This data is lost somehow by the time the page is rendered though. I'm not making any changes in _app.tsx to how the props are passed along. I am just passing the pageProps to the Component element.