curl -4 -I --max-time 15 https://xen-orchestra.com/ # HTTP/2 200
curl -6 -I --max-time 15 https://xen-orchestra.com/ # couldn't connect

What fixed it was disabling IPv6 at boot, then rebooting so xo-server starts with it already off:

printf '%s\n' 'net.ipv6.conf.all.disable_ipv6=1' 'net.ipv6.conf.default.disable_ipv6=1' | sudo tee /etc/sysctl.d/99-disable-ipv6.conf

After that, xoa check was green, including internet connectivity and no more check for upgrade issues. I'm hoping this fixes my XO Config Cloud Backup. I will report back if not.

17/17 - Internet connectivity: Error: HTTP connection has timed out
at ClientRequest.<anonymous> (/usr/local/lib/node_modules/xoa-cli/node_modules/http-request-plus/index.js:61:25)
at ClientRequest.emit (node:events:519:28)
at ClientRequest.patchedError [as emit] (file:///usr/local/lib/node_modules/xoa-cli/index.mjs:31:17)
at TLSSocket.emitRequestTimeout (node:_http_client:927:9)
at Object.onceWrapper (node:events:633:28)
at TLSSocket.emit (node:events:531:35)
at TLSSocket.patchedError [as emit] (file:///usr/local/lib/node_modules/xoa-cli/index.mjs:31:17)
at Socket._onTimeout (node:net:604:8)
at listOnTimeout (node:internal/timers:585:17)
at process.processTimers (node:internal/timers:521:7) {
url: 'https://xen-orchestra.com/',
originalUrl: 'http://xen-orchestra.com/'
}

XOA Update sometimes failed too but hitting Refresh a couple times got it going.
10/1/2026, 10:03:28 AM: All up to date
10/1/2026, 10:26:26 AM: Start updating...
10/1/2026, 10:26:32 AM: HTTP connection has timed out
10/1/2026, 10:27:14 AM: Start updating...
10/1/2026, 10:27:14 AM: stable channel selected
10/1/2026, 10:27:14 AM: All up to date