You could try and take a packet capture from the LAN side of your Meraki device to ensure that there is differently not an IP Conflict issue. Trying rebooting your Meraki device to clear any ARP cache or alternatively you may have to wait for it to clear itself.
We had a similar case generating alerts. A Thinkpad with Ubuntu. DHCP was assigning an IP to both NICs, wifi and ethernet. But if I understand correctly, the MX100 was also attributing both IPS to each NIC, resulting in alerts. Mind bending.
I know this is a very old post, but I am experiencing the same or similar with an Ubuntu Server. The Meraki alert is attributing the MAC address from each of the two NICs to the same single IP address we have assigned in the DHCP server to just one of the NICs.
I know this has something to do with "teaming" as we attempted to team the NICs on this system, but did not ever get it to complete fully. I suppose the alerts are evidence that some sort of teaming may be occurring since its detecting the MAC address change and alerting us.
I don't really have a solution yet, but this post has pointed me in the right direction. Thanks.