Thanks for the tips. All failed I'm afraid and spent hours troubleshooting further.
Failed connection attempts moved to throwing a Error: 18456, Severity: 14, State: 11.
States 11 & 12 mean that SQL Server was able to authenticate you, but weren't able to validate with the underlying Windows permissions. It could be that the Windows login has no profile or that permissions could not be checked due to UAC.
The brief update is, experienced the issues in the below articles.
Solution: After using many scripts, SSMS, checking UAC, .. etc. Discovered the AD Group had Status | Settings | DENY. Had not seen it before, don't know how it changed to this, and many scripts did not show. Script that did worked is below.
SELECT pr.principal_id, pr.name, pr.type_desc,
FROM sys.server_principals AS pr
JOIN sys.server_permissions AS pe
ON pe.grantee_principal_id = pr.principal_id;