so you're going to the server ip directly and then to the vip ?
Or do you always go to a vip ?
What is the content rule(s) involved ?
Can we see the config ?
Do you have more than 1 server ?
Maybe you are not loadbalanced to the same server when you open the 2nd connection and therefore the server rejects it.
You may need some form of stickyness.
Gilles.