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: https://sultan-kozhevnik.vercel.app But on my custom domain: https://www.sultan-kozhevnik.ru https://sultan-kozhevnik.ru 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: https://sultan-kozhevnik.vercel.app Custom domain: https://sultan-kozhevnik.ru https://www.sultan-kozhevnik.ru 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?