Using a load balancer with servers and the session information is shared between these servers.
The problem is that authentication does not happen when we change to the other IP resulting in the user being logged out and asked to authenticate again.
Users also may not be able to logout.
Configuration issue - The ip address being used in the load balancer is not a sticky IP.
The load balancer must have persistence enabled to ensure users always use the same proxy host unless in a failover situation. The 'persistence' ensures that a user is always using the same proxy, and thus the same session.
If the user switches proxy, then the session information will be lost and the user will have to log back in.
Persistence is also known as affinity or sometimes 'sticky ip'.