Failed to initialize LightningCSS: Failed to fetch — Preview not loading in Chrome - v0

Hi, Yesterday I was able to use my project environment without any issues, but today the preview panel shows nothing (blank / no output). I also tried switching back to older versions, but the problem still happens.

On my current computer I’m using Google Chrome, and I get this error:

Failed to initialize LightningCSS: Failed to fetch

However, on my other computer (using Opera GX) the preview works normally and I don’t see this error.

Do you know what could cause this only in Chrome and how I can fix it? I’m looking for steps such as what to check in Chrome settings (cache, extensions, blocked requests, CORS, service workers, etc.) or anything related to LightningCSS initialization.

Thanks.

Hmmmm…. not sure, but a few questions or thoughts around this (maybe you have tried all already though)

have you asked the v0 agent to look into this / fix this?
1. Have you tried this prompt: Try prompting v0 with: "The preview is failing to load due to a LightningCSS fetch error. Can you revert the CSS configuration or ensure the build doesn't depend on external WASM fetches for the preview?"
is your chrome browser up to date (latest build)?
Are you using a VPN by chance?
Have you tried a “hard reload” (Cmd+shft+R)…not sure what this is for Windows
Are you using any specific (or new) ad blockers which are activated
- LightningCSS often fetches its engine dynamically.
- Open the Network Tab in DevTools.
- Refresh and look for a red line ending in .wasm.
- If blocked, disable extensions like uBlock Origin or AdGuard for that specific site.
you can try this work around found in another chat. I am not sure if it is a definite “solve” but it seems to have helped a couple users. https://community.vercel.com/t/anyone-having-issues-with-a-black-screen-at-preview/21642/15?u=heystu

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Lets us know if any of the above works or if there is any more info you can provide.

Since you said it was workgin fine with Opera GX, I looked into that a bit and found the following (again you may have already done the same troubleshooting). Felt it was worth a shot to send in case you havent tried this.

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This behavior points to a Chrome-specific security blockade or a corrupted Service Worker within Chrome's local storage for v0.dev.

1. The "Ghost" Service Worker Fix

Chrome is more aggressive than Opera in caching "Service Workers"—scripts that run in the background to handle network requests. If a v0 update happened and your Chrome Service Worker is out of sync, it will fail to fetch the LightningCSS binary while Opera (on a fresh session) works fine.

In Chrome, open your v0 project.
Press F12 to open DevTools.
Go to the Application tab.
On the left sidebar, click Service Workers.
Check the "Update on reload" checkbox.
Click "Unregister" on any worker listed for v0.dev.
Refresh the page.

2. Reset Chrome's WASM Cache

Opera GX often has "Battery Saver" or "Network Limiting" features that bypass certain standard caching behaviors, which might be why it's avoiding the bug. Chrome might have a cached failed attempt at fetching the .wasm file.

While in DevTools, go to Application > Storage.
Ensure "Including third-party cookies" is checked.
Click Clear Site Data.
Important: Restart Chrome completely (don't just close the tab).

3. Check for "Safe Browsing" Interference

Chrome's "Enhanced Safe Browsing" sometimes flags binary .wasm fetches from subdomains (like v0's preview frames) as potential "unverified downloads."

Try turning it off temporarily: chrome://settings/security -> Set to No protection.
Refresh v0. If it works, you'll need to add an exception for Vercel.

4. Chrome Flag: WebAssembly JavaScript Promise Integration

If your version of Chrome recently updated to v131 or v132, there have been reports of changes to how WASM fetches integrate with JS promises.

Go to chrome://flags.
Search for WebAssembly JavaScript Promise Integration (JSPI).
If it is "Default" or "Enabled," try Disabled (and vice versa).