500: Failed to fetch dynamically imported module

[jakobsturm]

Describe the bug

I am encountering some issues when deploying my project to vercel using the vercel-adapter. The project builds but then the deployed site I receive 500 Failed to fetch dynamically imported module: https://xxx.vercel.app/_app/undefined

The vercel build is triggered by a new Gitlab commit.

Does someone have an idea what could cause this issue? The weird thing is that it works with npm run build but not on the deployed vercel site...

Reproduction

This should be reproducable by using the same sveltekit + adapter versions

Logs

No response

System Info

System:
    OS: Windows 10 10.0.19044
    CPU: (8) x64 Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
    Memory: 13.49 GB / 31.91 GB
  Binaries:
    Node: 16.13.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.4 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 8.3.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 97.0.4692.71
    Edge: Spartan (44.19041.1266.0), Chromium (97.0.1072.55)
    Internet Explorer: 11.0.19041.1202
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.10
    @sveltejs/adapter-vercel: next => 1.0.0-next.36
    @sveltejs/kit: ^1.0.0-next.225 => 1.0.0-next.225
    svelte: ^3.46.0 => 3.46.0

Severity

blocking all usage of SvelteKit

Additional Information

No response

[mawoka-myblock]

Having the same issue with cloudflare adapter, but just on reload.

[benmccann]

This should be reproducable by using the same sveltekit + adapter versions

I don't think this happens with all projects or we'd probably be getting a whole lot more bug reports. Can you make it happen with a brand new project? If not, can you provide a project that reproduces it?

[jakobsturm]

Thanks, @benmccann! Yes, you are probably right - sorry for my assumption.
I am trying to work out how to reproduce it and will update you further.

Additionally I have noticed, the first error I receive when loading the page is: 500: TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of URL. Received undefined and after that reload it is the error mentioned above.

But of course I understand that it is hard for you to reproduce it like that. I was just hoping that someone has already experienced the same issue and has a solution. I will keep you updated. Thank you!

[mawoka-myblock]

Here is the repo: https://github.com/mawoka-myblock/svelte-cf-error
And I deployed it for testing reasons here (ofc with cf-pages): https://svelte-cf-error.pages.dev/blog/test
If you visit the link directly, you'll get a 500 document undefined (Any tips here are really appreciated), but if you go to https://svelte-cf-error.pages.dev/blog and then open the blog-post, it works until you reload. The first reload will produce a 500 document not defined error and the 2nd reload the error this issue is about.

[netaisllc]

Just for a small bit of added context, we are deployed to our own VMs on Digital Ocean (plain old node adapter) and see this error in the logs approximately 1-2 per week. Still trying to gather enough of the situation to share. :(

[mawoka-myblock]

@benmccann It also happens on/with the clodflare-pages adapter

[ManuelDeLeon]

Getting the same error on a hello world app: https://github.com/ManuelDeLeon/sveltekit-firebase-ssr

It works as expected locally in dev and preview.

The problem is that when deployed to Vercel (https://sveltekit-firebase-ssr.vercel.app/) SSR doesn't work (page source isn't what's expected), an error flashes, and the console shows another error.

Error on page:

Failed to fetch dynamically imported module: https://sveltekit-firebase-ssr.vercel.app/_app/undefined

Error in console

Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/html". Strict MIME type checking is enforced for module scripts per HTML spec.

[mawoka-myblock]

Vercel works for me fine, but Cloudflare-Pages doesn't