Forwarding Virtual Servers, SNAT Pools, and Port Collisions

Yes, that is correct, the error occurs when the same IP/port pair is used on both ends, but we do always connect to the same remote IP and port. As for the connection calculation, the connections are all simple HTTPS connections, typically lasting in the area of 0.3 - 0.5 seconds. Your assumption on the SNAT pool is correct, it is only assigned and used by this single forwarding virtual, which connections only to a single remote IP. There are no NATs occuring outside of this single SNAT pool prior to the connection leaving the F5, so yes, no source NAT on the client address prior to them hitting the forwarding virtual.