Session value lost in Windows Authentication mode in IIS 10.0

Even though set the session timeout and IIS apppool ideltime out=540 some times Session data is getting null but most of the times session data is available.

Why some times getting this behavior. I am new to the web application development.

Suggest me how to avoid this issue.

In web.config:

<sessionState cookieless="false" mode="InProc" timeout="540"></sessionState>
<authentication mode="Windows">
</authentication>