Login of simultaneous multiple users on Different Systems

I am working on a webapp running on cloud server. I have multiple user login on it. The problem is if I login from user 1 on one system, then if login user 2 from another system, the first login of user 1 automatically switches to login of user 2. Please help.

 

I am using some static variable to save and access user information throughout the program but that static variable gets updated with new value when any new user logins from another PC or Browser.