Sessions & Application expiring too quickly

I see a very odd behaviour in Production Live: 

I have set the Session state element in web.config as Mode = InProc, Timeout = 20 (by default, which is in minutes)

When I deploy my application to the Live environment, the Session_End event raises very quickly, I say in 1 minute, which will result the Application_End to raise as well.

 So no matter how many users are online at a time, they application_end is raised in 1-2 minutes if no request comes to the application during that time. consequently, all the data stored in sessions are gone!

Any help or advise?
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