Session ends randomly after redirect

Question

I have a strange problem in ASP .NET MVC 4. In AccountController I am doing redirects on certain actions and put data into TempData (which is stored in Session) before that:

[AllowAnonymous]
public ActionResult Activate(string token)
{
    new CustomSignupService().Activate(token);
    TempData["Message"] = "User was successfully confirmed";
    return RedirectToAction("Message", "Home")
}

Now I know I could just return shared Message view in this case, but this is just a code sample to reproduce the problem.

CustomSignupService.Activate does a db lookup via NHibernate and updates user in transaction (user activation). Sometimes (lets say 1/5 tries in 5 minutes) TempData does not make it throught the redirect, so I added logging into Session_End and noticed that session ends when RedirectToAction is invoked. Right after that Session_Start is invoked but of course TempData is gone.

Session has default timeout (20min) and controllers use SessionStateBehavior.ReadOnly

Any ideas?

UPDATE

Step 1: It's not Application Pool recycling (I turned on all General Recycle Event Log entries on Application pool and checked event log, after session restarts but recycle is not causing it)

Answer 1

I had a problem with Session being lost. I used Fiddler and noticed that there was a duplicate ASP.NET session cookie with a blank value. I don't know how it got there. So a new session was created on every request. I deleted that duplicate cookie and the problem was solved.

Other unlikely reasons are:

IIS process recycle

Session.abandon being called

modifying bin folder or web.config causing app restart

Check out this page:

Losing Session State