Users losing their NTLM authentication

Hi All, I´m using FSSO collector installed on one of our Active Directory in pooling mode. If I have to add some mac address reservation  on wifi interface or change some aleatory config on FG, ALL users connected through NTLM loses their authentication. I think it´s a BUG and the Fortinet Support can´t solve so far. I´m using v5.0,build0318 (GA Patch 12) on FG 200-B in cluster mode Active-Passive. Earlier versions has the same problem. I don´t know how long time this is happening because only now I could reproduce the issue. I´m thinking in use RADIUS to try solve it, any idea ? Thanks,