Static assets stall on custom .ru domain, but work on .vercel.app

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1

Current versus Expected behavior

I have a Next.js site deployed on Vercel.
The exact same production deployment works correctly on the default Vercel domain:

But on my custom domain:

static assets fail to fully download or load extremely slowly. This affects JS, CSS, fonts, SVGs, and images — not only next/image.
Expected behavior:
Static assets should download normally on the custom domain, the same way they do on the .vercel.app domain.
Actual behavior:
The HTML document loads, but static assets on the custom domain stall during full GET body download. The page renders incorrectly because JS/CSS/fonts/images do not finish loading.

Code, configuration, and steps that reproduce this issue

Example failing asset:
https://www.sultan-kozhevnik.ru/_next/static/chunks/12.eg6ivi-u1j.js
HEAD request works:
curl.exe -I “https://www.sultan-kozhevnik.ru/_next/static/chunks/12.eg6ivi-u1j.js”
It returns 200 OK with:
HTTP/1.1 200 OK
Content-Length: 117100
X-Vercel-Cache: HIT
Server: Vercel
X-Vercel-Id: arn1::z7xvz-1777845227205-f719dc120d1a
But full GET stalls at around 17% / ~20917 bytes:
curl.exe -L “https://www.sultan-kozhevnik.ru/_next/static/chunks/12.eg6ivi-u1j.js” -o NUL
The same file on the default Vercel domain downloads 100% successfully:
curl.exe -L “https://sultan-kozhevnik.vercel.app/_next/static/chunks/12.eg6ivi-u1j.js” -o NUL
The issue also appears in the browser console as failed resource loads with:
net::ERR_CONNECTION_CLOSED
This happens for multiple asset types:

  • .js
  • .css
  • .woff2
  • .svg
  • images
  • /_next/image requests
    I also tried disabling Next Image Optimization temporarily, but the issue remained, so it does not seem specific to next/image.

Project information

Framework:
Next.js
Hosting:
Vercel Hobby plan
Default Vercel domain:

Custom domain:

DNS:
The domain is now using Vercel nameservers:
ns1.vercel-dns.com
ns2.vercel-dns.com
nslookup currently resolves sultan-kozhevnik.ru to:
216.198.79.65
216.198.79.1
Vercel shows the domain configuration as valid.
The root domain redirects to www:
sultan-kozhevnik.ru → 307 → https://www.sultan-kozhevnik.ru/
This looks very similar to this solved community case:
“Possible edge/custom-domain asset delivery issue” by whiplasssh, Apr 17
In that case, the .vercel.app domain worked, but assets on the custom .ru domain loaded extremely slowly or failed, with x-vercel-id on arn1 edge.
Could someone from Vercel check whether this is an edge/custom-domain asset delivery issue, possibly related to arn1 edge routing for the custom domain?

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.