Macintosh with Active Directory

Hi to all,  we are implementing a navigation restriction mechanism through Fortigate integrated with active directory that will allow the user to navigate to certain sites only if they are part of a certain global AD group.For microsoft clients we have no problem, but for mac clients we have the following problem: run the command net user xxxxxx / domain AD sees a last logon time wrong and does not correctly rest the group to which it belongs. We have already removed and recreated the machine account and also the AD user.
any suggestions?