Hi Vercel Community,

I have an intermittent connectivity problem with my Vercel custom domain.

Project: Tarana

Custom domain: https://www.taranagadzhieva.ru

Vercel deployment URL: https://tarana-seven.vercel.app

The Next.js application and deployment are working correctly through the Vercel deployment URL, but the custom domain intermittently fails to load.

The important part is that this happens from the same device and the same network.

For example, I tested the exact same static JavaScript asset:

Custom domain: https://www.taranagadzhieva.ru/_next/static/chunks/3p9eevrhj-twl.js

The server returns HTTP 200, but the transfer stalls after approximately 14 KB out of 227,314 bytes and eventually times out.

The same file through the Vercel deployment URL:

https://tarana-seven.vercel.app/_next/static/chunks/3p9eevrhj-twl.js

downloads completely (227,314 bytes) on the same device and network.

Chrome also reports: ERR_CONNECTION_CLOSED

I have already verified:

• Vercel deployment is Ready and Production.
• DNS configuration is valid.
• SSL/TLS certificate is valid.
• There is no AAAA record.
• VirusTotal reports 0/90 detections for the domain.
• The Vercel deployment URL works normally.
• The custom domain can sometimes work over mobile LTE or Wi-Fi, but can later stop working again without any deployment or DNS changes.

I also tested individual Vercel Anycast IPs using --resolve. The custom domain returns HTTP 200, but larger responses still stall during transfer.

Could anyone help determine whether this could be related to MTU/MSS, TCP packet loss/retransmissions, Anycast routing, or another network-path issue?

I would especially like to understand why the exact same asset downloads successfully from the vercel.app hostname but stalls through the custom domain.

I would prefer not to change the application or migrate the project unless there is evidence that the application is responsible.