What is the make and model number of the router?
For some reasons it seems that either the DHCP server is sending out the same IP address to two PLCs that are requesting IP address at the same time, or that both PLCs are picking the first assigned IP address from the DHCP server.
Is this repeatable?
We will try this on a different router to see if we get a different results.
Why is your router DHCP assignment jump from 130 to 161 when two devices are requesting DHCP simulataneously? Is it because there are other devices already been assigned 131 to 160?