Linux workstation joined to AD can't su to root

[dutsnekcirf]

I've joined several CentOS 6.8 workstations to an Active Directory domain and am able to login with my domain user account on all of them. Additionally I can successfully su to root (sudo su -) on all of the workstations...except for this one workstation in particular.

I've edited the /etc/sudoers file and added the following line:

%MYDOMAIN\\IT_Admins ALL=(ALL) ALL

I've verified that my user account is a member of the IT_Admins group in Active Directory and so it should be allowed to elevate to root. This is the same line used in all the other workstations I've added to the domain. And on all those other workstations I'm able to elevate to root just fine.

Is there something besides the /etc/sudoers file I need to look at?