Mobile iOS Safari Errors - 500: Importing a module script failed.

Describe the bug

I recently migrated my website from NextJS to SvelteKit.

Everything has worked smoothly except for mysterious errors that seem to happen mostly on mobile iOS Safari, but also on desktop Firefox.

On Safari, the error is: “500: Importing a module script failed.” On Firefox, the error is: “500: error loading dynamically imported module”

As you can see, this is so common that a total of 0.6% of visitors are getting a critical error that is severe enough to replace the entire page’s content with an error message.

On Safari, the error happens mostly on the home page. On Firefox there is no noticeable pattern. It appears to be a client-side error because my Vercel server logs are not picking up the errors.

I track the error by sending a custom event to Plausible Analytics in the __error.svelte file.

The error appears to be coming from up-to-date browser versions. As in, Safari 15 and Firefox 101.

Here’s the spike in errors after switching to SvelteKit:

Unfortunately, I am totally unable to replicate the error myself. It does not show up on my iPhone or the versions I tested with Browserstack. And there doesn’t appear to be any stack trace provided to help me debug the issue.

This is my site: https://stockanalysis.com/ This is the repo: https://github.com/stockanalysisdev/stock-analysis-sveltekit

Has anyone dealt with this issue before? Or have an idea about the best way to debug the issue without being able to reproduce it myself?

Also, if anyone could try visiting my home page on mobile iOS Safari and see whether they get an error and a stack trace then that would be incredibly helpful.

Reproduction

Unable to reproduce testing on my own iPhone or via Browserstack.

Logs

No response

System Info

All packages have been updated to their latest versions.

System:
    OS: macOS 12.4
    CPU: (10) x64 Apple M1 Pro
    Memory: 333.49 MB / 32.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 17.9.0 - /usr/local/bin/node
    npm: 8.8.0 - /usr/local/bin/npm
  Browsers:
    Brave Browser: 102.1.39.122
    Chrome: 102.0.5005.115
    Firefox: 101.0.1
    Safari: 15.5
  npmPackages:
    @sveltejs/adapter-auto: 1.0.0-next.50 => 1.0.0-next.50 
    @sveltejs/kit: 1.0.0-next.350 => 1.0.0-next.350 
    svelte: ^3.48.0 => 3.48.0

Severity

blocking an upgrade

Additional Information

No response