Dynamic imports sometimes fail after deployment, app stuck at `Loading...`

Describe the bug

Description

I have a long-running SvelteKit app (maintained and upgraded regularly for 2+ years).

Recently, after adding async Svelte components and remote functions, the app works normally in most cases.
However, sometimes after deployment, the new version gets stuck at Loading... (I have SvelteKit boundary with a pending snippet in +layout.svelte).

• Refreshing does not resolve it.
• Issue appears browser-specific (seen on Samsung browser on mobile).
• Clearing cookies/cache fixes it.
• Different browsers load the site fine.

Logs from chrome://inspect (some parts are cleaned up)

GET /_app/immutable/chunks/DL90h7xO.js net::ERR_ABORTED 404 (Not Found)

TypeError: Failed to fetch dynamically imported module: /_app/immutable/nodes/0.FB441CHC.js
at handleError (app.js:2)
at J (runtime.js:2)
at fr (runtime.js:2)
at kr (runtime.js:2)

Uncaught (in promise) TypeError: Failed to fetch dynamically imported module: /_app/immutable/nodes/0.FB441CHC.js

Notes

• This seems to happen when the browser has cached an old version of assets.
• Clearing cache allows the app to load correctly.
• Possibly related to immutable asset caching, dynamic import resolution, or deployment cache invalidation.

Expected behavior

After deployment, the app should not fail to load due to missing dynamic import chunks.

Reproduction

The issue is difficult to reproduce and happens randomly.

Logs

System Info

System:
    OS: macOS 26.0
    CPU: (8) arm64 Apple M1
    Memory: 151.78 MB / 8.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.18.0 - ~/.nvm/versions/node/v22.18.0/bin/node
    npm: 10.9.3 - ~/.nvm/versions/node/v22.18.0/bin/npm
    pnpm: 10.3.0 - ~/.nvm/versions/node/v22.18.0/bin/pnpm
    bun: 1.2.21 - ~/.bun/bin/bun
  Browsers:
    Chrome: 140.0.7339.133
    Safari: 26.0
  npmPackages:
    @sveltejs/adapter-node: ^5.3.2 => 5.3.2 
    @sveltejs/kit: 2.38.1 => 2.38.1 
    @sveltejs/vite-plugin-svelte: ^5.1.1 => 5.1.1 
    svelte: ^5.38.10 => 5.38.10 
    vite: ^6.3.6 => 6.3.6

Severity

annoyance

Additional Information

No response

Start with the pending snippet in +layout.svelte and the dynamic-import errors reported from app.js and runtime.js. Reproduce a deployment with cached immutable assets, paying attention to the missing chunks and Samsung Browser behavior. Done means a deployed app no longer remains stuck at Loading when an older cached version requests unavailable dynamic-import assets.