asp.net 4.5 sessions lost and back after seconds

[franck37]

I have a very strange problem with ASP.NET 4.5 Sessions on Windows 2012Description:Sessions work fine. I go through the site, login, access eg profile and other aspx pages which use the session. then from one second to another, on any aspx page, the session get lost, on every aspx page. after some seconds, the session is back. So if i am logged in before the problem appeared, i lost the session values, and after some seconds they are back.This happens with every Browser (IE, FF, Chrome).I did yet tryd to user InProc, State Server, Appfabric, but with all the same, so must have to do something with the .net Session Handling on "toplevel" or with the IIS, whatever...not sure about, but mostly, subjectivly i think the requests are very slow right before the session get "lost". Crazy, that they "come back" after... so they are not really lost.Any idea ?