Dual Gig Ethernet board - zero response from any device connected to eth1 but only with both ports occupied


I recently got the reRouter w/ dual gigabit ethernet carrier board. I installed raspbian in emmc. I am trying to use both eth ports as p2p tcp connections to two other devices. no router nor dhcp involved. Everything has static IP. I am using ping to test the connection but no matter which device - anything plugged into eth1 cannot be communicated with as long as any device is connected on eth0. (those same devices that fail when connected to eth1 work fine when connected on their own but also when connected to eth0 and eth1 is occupied)

device0/eth0 and device1/eth1 = ping device0/eth0 fails & ping device1/eth1 works
device1/eth0 and device0/eth1 = ping device1/eth0 fails & ping device0/eth1 works
device0/eth0 and nothing/eth1 = ping device0/eth0 works
nothing/eth0 and device0/eth1 = ping device0/eth1 works
device1/eth0 and nothing/eth1 = ping device1/eth0 works
nothing/eth0 and device0/eth1 = ping device0/eth1 works

Are eth0 & eth1 handled differently?

Anyone else try to set up both ports as simple static ip p2p connections with 2 other devices?

still havent figured this out, and i feel like im going crazy testing the same things over and over.

pinging device on eth1 port fails any and every time eth0 is also occupied.