Large static files fail to download via custom domain but work via .vercel.app

Help
1

I’m experiencing an issue where large static JavaScript files fail to download when accessed through my custom domain, but work perfectly fine through the .vercel.app domain.

Project details:

Issue:

When requesting the main JS bundle through the custom domain, the HTTP headers return successfully (status 200, correct content-length), but the actual file content either:

  • Times out with 0 bytes received

  • Times out after receiving only ~10KB of ~1.7MB

Affected URL (custom domain - FAILS):

https://adminas.org/assets/index-BZZFp_s8.js

  • x-vercel-id: fra1::btchs-1767769066740-7d315e69c4f6

  • content-length: 1751057 (1.7MB)

  • Result: Timeout, 0 bytes received

Working URL (.vercel.app - WORKS):

https://adminas-frontend-git-beta-lumpovs.vercel.app/assets/index-BZZFp_s8.js

  • x-vercel-id: fra1::rw6vp-1767769075594-be105d0dabeb

  • content-length: 1751057 (1.7MB)

  • Result: Downloads successfully in ~1.2 seconds

Additional observations:

  • HTML page (https://adminas.org/) loads correctly (965 bytes)

  • CSS file (https://adminas.org/assets/index-B3tInvv7.css, 2.8KB) loads correctly

  • Only large files (JS ~1.7MB) fail to download

  • Browser shows ERR_HTTP2_PING_FAILED error

  • Issue persists regardless of DNS provider (tested with Cloudflare DNS and Vercel nameservers)

  • Same edge region (fra1) is used for both domains

Expected behavior:

Static files should download identically whether accessed via custom domain or .vercel.app domain.

Steps to reproduce:

  1. Open browser DevTools → Network tab

  2. Navigate to https://adminas.org/

  3. Observe that HTML loads, but JS file stays in “pending” state indefinitely

2

The domain troubleshooting guide can help with most custom domain configuration issues. You might be able to use that guide to solve it before a human is available to help you. Then you can come back here and share the answer for bonus points.

You can also use v0 to narrow down the possibilities.

5

Are you using a VPN or any antivirus software? The ERR_HTTP2_PING_FAILED is usually caused by something intercepting the request, like TLS inspection or vpn reconnection

Can you reproduce this on other devices or networks?

6

The error ERR_HTTP2_PING_FAILED does not always appear in Dev tools. Most often (failed)net::ERR_TIMED_OUT.

What I’ve Already Tried:

  1. Removed and re-added the custom domain multiple times

  2. Switched nameservers to Vercel DNS (ns1.vercel-dns.com, ns2.vercel-dns.com)

  3. Tested with Cloudflare DNS (CNAME to cname.vercel-dns.com, DNS only)

  4. Verified SSL certificate is valid

  5. Removed all custom headers from vercel.json

  6. Tested from multiple networks — issue persists

Request:

Could you please investigate why the Vercel Edge servers assigned to custom domains (IP range *.65) fail to deliver response bodies, while the servers assigned to .vercel.app domains (IP range *.131) work correctly?

Vercel IDs for reference:

  • Custom domain request: x-vercel-id: fra1::* or arn1::*

  • Project: adminas-frontend

  • Custom domain: adminas.org