Persistance session Idle time out issue

A persistence profile can have a timeout value, and many of them do have fairly short idle timeouts. If persistence was the problem, users would potentially get re-load balanced to other servers in the pool. What kind of persistence are you using now?

Otherwise, keep in mind that the TCP session that a client maintains with the BIG-IP (proxy) is not the same TCP session that the BIG-IP maintains with the server. Anything that happens at layer 7 though (ie. HTTP) is generally between the client and server directly.