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.