When running a Web Agent and when user <user1> accesses a resource, then its session gets later used for user <user2>.
To prevent SMSESSION to be cached in proxies, the ExpireForProxy and ProxyTrust will help as stated in the documentation (1).
Read carefully the documentation as other parameters are needed to be set along with these.
Further, as there's a Load Balancer, implement the stickiness feature (2).
If possible, to prevent more than 1 IP to use it, implement IP check for the cookie (3)(4).