I've got a number of Raspberry Pi 3 Model B's running Raspbian-Jessie-Lite (2017-04-10) that I've been trying to test switching the micro SD card between. I can have a Pi up and working perfectly and then replace it exactly with another Pi 3 and the Ethernet stops working. Everything else seemingly works fine.
With the Pi connected to a gigabit switch, the Pi will identify as 100M when working correctly. When switching to another Pi, it typically doesn't bring the interface up at all (according to the switch - although ifconfig reports it does) or it comes up as 10M (again - according to the switch).
As per the suggestion here, I checked /etc/udev/rules.d/ but didn't see a 70-persistent-net.rules file. It would seem that something unique to each particular piece of hardware (like a MAC address) might be getting set somewhere in the OS and causing issues. Is there anywhere else I should check to see if the address is being set or any other suggestions?