@Naresh Welcome to the Atlassian community
I am assuming that you are already logged into Confluence and opening multiple pages that you have either bookmarked or can otherwise reach them through additional tabs. I have seen this before when individuals are not logged into Confluence first and try to open pages. Can you confirm that you are already logged into Confluence in the browser you are trying to open the pages? Can you also confirm that after you login and open all the tabs that this issue is not happening after you have not been active in Confluence in that browser for some time.
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