Hi Pinki -

This is completely expected. If you login to your bank's website and then step away for 10-15 minutes, the session is closed. Tableau does the same thing with your session against Tableau Server. Keep in mind that an open session against any web application uses resources, so most web apps are going to do something like this. When we kill your session, your filter selections are lost. So, when you interact with the viz "later", it gets re-rendered from "zero".

If you need the behavior changed, your server admin can make a server-side modification that will extend the session time-out - but doing this COULD impact performance if lots of "old" sessions are allowed to hang around.