I don’t think MAC address is the problem, because first of all, MAC address is never exported and imported, second, firmware 2.0.9 and 2.1.0 use the same software defined MAC address, so it should remain the same. The only thing that may change is the Device ID, which defines the last byte of the MAC address. If you have ever changed the Device ID (default is 0), that may have affected the IP address.
If you can log on to the router’s configuration page, can you tell if the MAC address has changed before and after installing 2.1.0?