Domain group hierarchical group membership and SQL Logins mapped to AD groups
This answer may not be of any real value since now the question becomes WHY is there a lag... 

but the AD changes were done 3 days ago and in my particular case, it took 3 days before SQL Server started recognizing the new members/groups added.

As of last night, when i executed EXEC xp_logininfo 'DOMAIN\User1','all' it returned nothing.. today (4th day since change) it shows the permission path as 'DOMAIN\GroupA'.