Default MAC address the same on multiple Firewalls

Hello Sophos Community,

I am in the process of setting up two firewall clusters, one with two XG210's and one with two XG230's. I have configured port 1 on these devices as the 'management' port which I want to restrict access to the web portal. It is on subnet that has been isolated within our environment to only be used for device management.

The XG210 has been configured with a X.X.X.6 address and the XG230 has been configured with X.X.X.8.

I am having troubles connecting, the connections are very slow and sometimes it won't connect at all. I have discovered that the both firewalls have the same MAC address for port 1 which is obviously causing problems on the switch ARP table. As we can see here, the same MAC is in the ARP table twice for the different IP address:

I have also confirmed that the firewalls are showing the same MAC address:

XG210:

XG230:

Can someone explain to me why two separate physical devices have the same MAC address? I would have thought the default MAC address for two physical devices would have been unique.

I do understand that I can override the MAC address, but I would like to understand why they are the same and I don't want to have to manage the MAC address of my firewalls.

Thanks,

Tim