After PPM 14.3, PPM does not create the JSESSION cookie below /niku anymore. Before this change each app could share a proxy and each proxy could LB between all the app nodes. now you can have one proxy per app and each proxy can only connect to it one app node.
This means that using Apache as a load balancer will not work to have reliable sticky sessions.
We recommend to change the configuration so that sticky session gets enabled at the top F5, then silo down thru Apache proxy having each app configured with a dedicated Apache SSO proxy.