Vercel CDN: HTTPS connections close after 17–24 KB on Windows — ERR_CONNECTION_CLOSED - Help

Hello Vercel Community and Vercel Networking Team,

We need assistance investigating a persistent HTTPS/CDN connectivity issue affecting our project.

Project: ADOKVA
Team: adokvas-projects (Hobby)
Production: https://www.adokva.com

ADOKVA — One Earth. Human Connections.

Choose the places that shaped your life, see your path on a living Earth, and compare selected places with someone you know. No account. No GPS. Your journey is stored locally; sharing happens only when you choose it.

Preview: https://adokva-ak35zpy9q-adokvas-projects.vercel.app/ru?view=path

Problem

Since late September 2026, our production site and Vercel Preview deployments have experienced repeated HTTPS connection failures on Windows computers.

Chrome / Edge: ERR_CONNECTION_CLOSED
Firefox: PR_END_OF_FILE_ERROR
iPhone Safari over LTE: working
Linux / cloud-based requests: HTTP 200
Some larger JavaScript transfers terminate after approximately 17–24 KB.

This is not simply a failed application build. Our latest Preview passed 271/271 tests and has deployment status READY, but that does not mean the website is accessible from affected Windows networks.

What we have verified

Vercel's support agent confirmed:

DNS configuration is valid.
The www CNAME is c62de010429e7031.vercel-dns-017.com.
The domain resolves to Vercel ingress IPs 216.198.79.65 and 64.29.17.65.
The SSL certificate is valid.
Vercel ingress returns HTTP 200.

We also previously observed that connectivity through the legacy Vercel IP 76.76.21.21 appeared to work at least once.

We tried independent hosting paths, including Cloudflare Pages and Workers, without achieving reliable access from the affected Windows computers.

We have not established whether the cause is CDN ingress routing, ISP interference, TLS inspection, packet loss, MTU/fragmentation, or another network-path issue.

Request to Vercel engineers

Could someone from Vercel's networking/CDN team help investigate:

Whether particular Vercel ingress IPs or network paths are affected.
Whether the observed 17–24 KB truncation matches known CDN/network issues.
Whether a supported alternative ingress or routing configuration can be tested without changing production DNS.
What minimal additional evidence would be most useful for diagnosing this issue.

We are on the Hobby plan and cannot upgrade to paid support. The official support agent directed us to the community.

We would appreciate any technical guidance or escalation to the appropriate networking team.

Thank you for your help.