That appears to have been the problem. RTEnIpFwrd was set to 0. I changed it back to 1 and then was able to change NatItf back to 3 and communication appears to be working again.
On that topic; what is the correct setting for for this setup for the NatItf parameter involving the 7 Cosy 131s connecting to the eFive 25? I don’t really understand the difference between 1 (NAT and TF on VPN) and 3 (NAT on LAN (Plug’nRoute)). Documentation for the Cosy/eFive setup seemed to point to 3 for Plug’nRoute and it appears to be working but the documentation for this setup also seems a little sketchy. Any other info on that - or am I okay where I am at now?