Direct connection routing with 3x ConnectX-4 Lx EN

I have 3 servers with ConnectX-4 adapters that I am trying to direct connect (no switch) using both ports on each card in a triangular topology. I have set unique static IP addresses on each port (6, all on the same subnet) and I can ping between the addresses on two of the three adapters but the third adapter is unable to echo the ping request to either of the other two (although tcpdump shows that the requests are received, and all interfaces are active and link connections are good).

How can a directly connected interface NOT be able to ping the other? Do I need to build route tables between the 6 addresses? What is the right way to get the 3 adapters (6 interfaces) talking?

Any help or guidance is appreciated.