Update:
The issue affects both custom domains:
The default Vercel domains work normally:
I ran the Vercel connectivity debug script for both domains. The results are consistent.
Some Vercel edge IPs fail:
216.198.79.1 timeout / 100% packet loss
64.29.17.1 timeout / 100% packet loss
Other Vercel edge IPs work and return HTTP/2 200:
216.198.79.65
216.198.79.129
216.198.79.193
64.29.17.65
64.29.17.129
64.29.17.193
Location:
Brazil, Mato Grosso
ISP:
NEOPRINT INTERNET LTDA
This confirms that the problem is not project-specific and not DNS configuration. It appears to be an intermittent routing/connectivity issue to specific Vercel Anycast edge IPs from this region.