Prerendered server route not found

[WaveLinkdev]

Describe the bug

When using fetch on a server route, that is pre-rendered (export const prerender = true), the operation fails with a message of not found. It can't be requested externally either ie. through the browser. This only occurs when using the built version.

Reproduction

https://www.sveltelab.dev/s3p4ypow5f1hy0u

Run using

npm run build
npm run preview

Logs

TypeError: fetch failed
    at fetch (file:///home/httpswwwsveltelabdev-n1l0/node_modules/undici/index.js:109:13)
    at async resolve (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:2663:14)
    at async respond (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:2529:22)
    at async fetch (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:2291:20)
    at async Object.eval [as fetch] (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:2230:12)
    at async load (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/entries/pages/_page.server.js:15:15)
    at async load_server_data (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:540:18)
    at async eval (file://file:///home/httpswwwsveltelabdev-n1l0/.svelte-kit/output/server/index.js:1900:18) {
  cause: HTTPParserError: Response does not match the HTTP/1.1 protocol (Content-Length can't be present with Transfer-Encoding)
      at Parser.execute (file:///home/httpswwwsveltelabdev-n1l0/node_modules/undici/lib/client.js:577:15)
      at Parser.readMore (file:///home/httpswwwsveltelabdev-n1l0/node_modules/undici/lib/client.js:518:12)
      at Socket.onSocketReadable (file:///home/httpswwwsveltelabdev-n1l0/node_modules/undici/lib/client.js:945:10)
      at EventEmitter.emit (https://httpswwwsveltelabdev-n1l0.w-corp.staticblitz.com/blitz.9c8944bc.js:35:156830)
      at emitReadable_ (https://httpswwwsveltelabdev-n1l0.w-corp.staticblitz.com/blitz.9c8944bc.js:35:729152)
      at _0xe8552e (https://httpswwwsveltelabdev-n1l0.w-corp.staticblitz.com/blitz.9c8944bc.js:44:152768)
      at https://httpswwwsveltelabdev-n1l0.w-corp.staticblitz.com/blitz.9c8944bc.js:44:152515 {
    code: 'HPE_UNEXPECTED_CONTENT_LENGTH',
    data: '{"data":"Test Data"}'
  }
}

System Info

(Github Codespace)
  System:
    OS: Linux 5.4 Ubuntu 20.04.6 LTS (Focal Fossa)
    CPU: (2) x64 Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz
    Memory: 1.22 GB / 3.84 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 19.9.0 - ~/nvm/current/bin/node
    Yarn: 1.22.19 - /usr/bin/yarn
    npm: 9.6.3 - ~/nvm/current/bin/npm
  npmPackages:
    @sveltejs/adapter-auto: ^2.1.0 => 2.1.0 
    @sveltejs/adapter-vercel: ^2.4.3 => 2.4.3 
    @sveltejs/kit: ^1.18.0 => 1.18.0 
    svelte: ^3.59.1 => 3.59.1 
    vite: ^4.3.8 => 4.3.8

Severity

serious, but I can work around it

Additional Information

This was already an issue that was apparently resolved
#8341
#8039
#8331

Supposed to be fixed in #8453

Also discussed on the discord server.

[WaveLinkdev]

Okay I'm sorry, this seems to be my fault. The error seems to be something else. Even tho we did have some issues on the discord server, this probably doesn't have anything to do with it. Although, I did have this problem, it seems to have been solved by some experimentation. Sorry for all the confusion, for stealing a pretty cool issue number and wasting your time. I love you all.

I will now close the issue, and please don't stone me to death, even tho I probably deserve it.