The message is reporting that option code 3072 was set in an arp the device received. I have not been able to find any information on this option other than what you have pointed out. What is the end device that sent the arp? That may give us a clue.
Thanks guys. As this is a Layer2 switch, my guess is that the ARP messages are coming from the default-gw for the VLAN where the switches are inside for management. Which is a Fortinet Firewall. But we will run a packet sniffer as soon as we find a free minute... will keep you updated.