FSSO troubles, may be linked to Windows Server 2016 Domain Controller ?

[chrbar]

Hello, We use FortiGate 3700D running FortiOS v5.2.3 build670 (GA), managed from FortiManager v5.2.2-build0706 150415. We use a FortiAuthenticator v4.00-build0019-20151007-patch00, set as FSSO (Fortinet Single Sign-On) with Windows AD Domain Controller polling. We meet some troubles with FSSO: authentications go up and down after some seconds. It look like the FortiAuthenticator receive FSSO Logon followed by FSSO Logoff. The changes that we did before this problem, are: - remove a DC (one on six), all under MS Windows Server 2012 R2, - add a new DC, a MS Windows Server 2016 (the first one of our DC infrastructure), - upgrade the past removed Domain Controller to MS Windows Server 2016, and add it (at the end, there is seven DC, including four MS Win Svr 2012 and two MS Win Svr 2016). Is there some known issues/troubles between FortiAuthenticator v4 and MS Win Svr 2016 (or DC running Win 2016 server)? Does someone run an identical infrastructure as us? If yes, did you meet some problems? If not, do you have any idea about these troubles? Thanks. Regards, Chris