To reproduce: In Chrome > Settings > Privacy and security > Advanced > Use secure DNS, select Cloudflare (1…1.1.1). Browse to www.bt.com and click “Email” at the top right. See “This site can’t be reached”.
This is confirmed at signin1.bt.com down? Current problems and status.
Site can however be reached by selecting “Google (Public DNS)” instead in Chrome settings.
Does anyone have an explanation or a solution?