Getting "Not found: /_app/immutable/...." on Vercel deployment even though the file exists

[grantjayy]

Describe the bug

In a production deployment on Vercel, I'm getting logs from my handleError function in hooks.server.ts saying that some routes in the .vercel/output/static/_app/immutable/assets/ are not found, even though they are in the folder. This also only happens on a couple of requests every few hours (on a small-medium site).

My setup is:

@sveltejs/kit - 1.0.0-next.504
@sveltejs/adapter-vercel - next
My handleError function is very basic and just logs the error.

Here is an example of a route that is not found:

Not found: /_app/immutable/assets/_layout-ff3a027e.css

Here are some screenshots showing the file exists:

The requests are also not coming from bots and are indeed real user agents.

I don't know if this is a bug or something else. Does anyone have an idea of what might be happening?

Reproduction

New svelte kit project with vercel adapter, push to vercel.

Logs

{"error":"Not found: /_app/immutable/assets/_layout-ff3a027e.css"}

{"error":"Not found: /_app/immutable/assets/+layout-583477e6.css"}

{"error":"Not found: /_app/immutable/chunks/singletons-f2af6dd9.js"}

{"error":"Not found: /_app/immutable/components/pages/video/_page.svelte-a44f8798.js"}

{"error":"Not found: /_app/immutable/chunks/1-94989325.js"}

System Info

System:
    OS: macOS 12.5.1
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
    Memory: 20.71 MB / 32.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 16.16.0 - ~/.nvm/versions/node/v16.16.0/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v16.16.0/bin/yarn
    npm: 8.15.0 - ~/.nvm/versions/node/v16.16.0/bin/npm
  Browsers:
    Brave Browser: 105.1.43.88
    Chrome: 105.0.5195.125
    Firefox: 104.0.1
    Safari: 15.6.1
  npmPackages:
    @sveltejs/adapter-vercel: next => 1.0.0-next.77 
    @sveltejs/kit: ^1.0.0-next.504 => 1.0.0-next.504 
    svelte: ^3.48.0 => 3.50.1 
    vite: ^3.0.3 => 3.1.3

Severity

annoyance

Additional Information

No response

[dummdidumm]

Does this still happen with the latest version of the Vercel adapter and SvelteKit? Is this maybe related to you deploying a new version and existing browser connections which are still on an old version try to load no-longer-available assets? Also see https://kit.svelte.dev/docs/configuration#version

[dummdidumm]

Closing due to inactivity; this may have been fixed. If not, please open a new issue.