Too Many Redirects error with ISR and optional route params

[adrienpicard]

Describe the bug

Possibly related to https://github.com/sveltejs/kit/issues/9459 but I'm receiving a "Too Many Redirects" error when using ISR with the Vercel adapter.

The route structure is /[first]/[[second]] and I'm getting the error when directly visiting URLs with only the first parameter.

Reproduction

https://kit-isr-demo.vercel.app https://github.com/adrienpicard/kit-isr-demo

Navigating to /lorem or /ipsum from the homepage works but not if you access the page directly or hard refresh.

Logs

---

System Info

System:
    OS: macOS 12.6
    CPU: (10) arm64 Apple M1 Pro
    Memory: 97.77 MB / 16.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 16.18.1 - ~/.nvm/versions/node/v16.18.1/bin/node
    Yarn: 1.22.19 - /opt/homebrew/bin/yarn
    npm: 8.19.2 - ~/.nvm/versions/node/v16.18.1/bin/npm
  Browsers:
    Chrome: 114.0.5735.106
    Firefox: 114.0.1
    Safari: 16.4
  npmPackages:
    @sveltejs/adapter-auto: ^2.0.0 => 2.1.0 
    @sveltejs/adapter-vercel: ^3.0.1 => 3.0.1 
    @sveltejs/kit: ^1.5.0 => 1.20.2 
    svelte: ^3.54.0 => 3.59.1 
    vite: ^4.3.0 => 4.3.9

Severity

blocking all usage of SvelteKit

Additional Information

No response