You could simplify the configuration and not use a lease pool. Have all client connect to one SNAT IP via a SNAT pool, applied to the VIP, instead of "AutoMap". --Local -> Address Translation --> SNAT Pool. That way you take out a layer of "complexity" knowing it is not a DHCP lease issue.
Network Configuration
--If you have a SELF IP for every Subnet needed for all of your applications/VIPs, then the clients will be able to route to where they need, as long as they have an IP that is one of the Self IP subnets you have configured. The F5 is a Layer 2("switch"), if it does not own the .1, where the routing will traverse the respective Self IP, versus the Default Route, if an IP is not matched.
iRule idea --
Try "when HTTP_RESPONSE_RELEASE" versus "when CLIENT_ACCEPTED"