I don't have a config backup from my old 5.2 machine. But I don't recall making any manual changes to anything.

(And also I don't think your hypothesis about access is correct. As I mentioned, other computers on the network have no issue with this. My Linux Mint PC wth a static address and my Windows laptop on DHCP are both able to receive responses to pings sent to the jails, and vice versa. Yet the jails are invisible to the gateway.)

I have already configured port forwarding for Transmission to the jail's IP address 192.168.1.12, as I had before with 5.2. Naturally, until ClearOS can be made to see this address, it is not functioning.