404 Page not found is thrown if using ISR in route with slug

[tonprince]

Describe the bug

I have the following page structure: /Transfers/From-[from]/To-[to]/By-[by]

Under the page folder By-[by] I added a +page.server.js with ISR enabled:

export const config = {
  isr: {
    expiration: false,
    bypassToken: BYPASS_TOKEN,
    allowQuery: []
  }
};

When I run the application locally with npm run dev or npm run preview the page is found and rendered correctly. But when deploying to Vercel a 404 error is thrown.

Reproduction

Visit https://sveltekit-isr-demo.vercel.app/Transfers/From-Krabi-sss/To-Samui/By-Train
Github: https://github.com/tonprince/sveltekit-isr-demo

Logs

No response

System Info

System:
    OS: macOS 13.2.1
    CPU: (8) arm64 Apple M2
    Memory: 144.55 MB / 8.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 18.13.0 - ~/.nvm/versions/node/v18.13.0/bin/node
    npm: 8.19.3 - ~/.nvm/versions/node/v18.13.0/bin/npm
  Browsers:
    Chrome: 111.0.5563.64
    Firefox: 111.0
    Safari: 16.3
  npmPackages:
    @sveltejs/adapter-vercel: ^2.4.0 => 2.4.0 
    @sveltejs/kit: ^1.12.0 => 1.12.0 
    svelte: ^3.57.0 => 3.57.0 
    vite: ^4.2.1 => 4.2.1

Severity

blocking all usage of SvelteKit

Additional Information

No response

[tonprince]

When I use the [...slug] syntax it seems to work but there is another issue when trying to read the slug and use it to load a firestore document. It strangely contains the '/__data.json' suffix when I click on a link which points to this ISR route.

As a workaround I just remove this suffix in order to get the url.

export const load = async ({ params }) => {
    let url = `/Transfers/${params.slug}`;
    url = url.replace("/__data.json", "");
    ...
    // load data from firestore with url
})

[dummdidumm]

When looking at what the SvelteKit runtime is invoked with it's /Transfers/Krabi-sss/Samui/Train - the static parts of the route segments are missing.