Have you looked at your return path, i.e. the path the traffic will take from the server back to the client?
For the CSS to work properly, it needs to see the traffic in both directions. If the path through the CSS is not the optimal path for return traffic (or you are in a "one-armed" configuration) you will need to setup a source group with a VIP address that makes sense for your scenario and add your service as destination services in the group.
This will result in the CSS NAT'ing the source address of clients before the sessions are forwarded to the backend server, thereby forcing the return traffic through the CSS. Hopefully, your server app doesn't need to see the true client IP addresses, (most don't). If it does, you'll need to place the CSS in-line between the client(s) and server(s) from either a L2 or L3 perspective.
