unbalanced pool , persistence problem

I'm no expert on persistence, believe me. But I bet you have it correct. Proxies are designed to pipeline the HTTP client requests into a relatively small number of TCP connections on the web server side. What you might want to consider is applying a OneConnect profile to the VIP. You should read the doc on it, but the way I think about OneConnect, it's a way for the LTM to load-balance at an HTTP session level versus the TCP level. With OneConnect, the LTM can distinguish between HTTP clients based on the information in the HTTP requests, rather than at the TCP level. We had to enable this with a VIP used by a small group of users behind a proxy server. We found that users would intermittently get forwarded to the wrong webserver, despite cookie persistence, because the proxy server would suddenly decide to establish a new TCP session and switch HTTP requests from the same user between them. This broke the persistence intermittently. With OneConnect, the LTM load-balances each HTTP request versus TCP connection. So we have concluded that it only makes sense to load-balance multiple pool members using cookie persistence with OneConnect - without it you are at risk of breaking persistence. The LTM config guide does a better job at explaining this.