When using a load balancer you must make sure your load balancer has "persistence" or is "using the sticky bit." This is to make sure that a login attempt goes back to the same server that was initially contacted for the login. However in this case, session persistence was already configured.
When I set up the F5 load balancer and because Web Viewer was using both the mainframe and LDAP, it was using an AUTH.
They were in a default snap pool and this was using source network address translation (SNAT) which resulted in a different ip causing problems for Web Viewer.
I changed to a dedicated snap pool where source network address snap converts to the same ip address and this resolved the problem.