I'm having same issue since yesterday with Firefox, on desktop, and mobile
https://oauth.virginmedia.com/as/AiaswrUstc/resume/as/authorization.ping
Pretty sure this is due to eMails being "Normal Password", not oath2
As my normal browser is Pale Moon, and that auto logs me in to the My Virgin Media site (cached Passwords likely still working from previous logins), but fails to find the email server.
Pale Moon can't find the server at mail.virginmedia.com.
So you've updated the EMail security, but not done that for old logins, mine being an NTLWorld eMail address.
When I joined in 2005 the original eMail, was the only one accepted for login.
This is the only "ViirginMedia" email account I have, and don't want to try to change things, and get locked out completely. Edit to clarify, I have 3 NTLWorld eMails, and this one on the forum is VirgiinMedia, but all use "Normal Passwords".
Thunderbird my eMail client has the ability to set the password security to Oath2, but that didn't help, whivh suggests the normal passwords are still used, but not accepted by the system.