A high volume of Magic ARP packets, received on network interfaces, may impact on the ARP Hit Rate of UTM appliances.
Meraki APs use a "Magic ARP" to inform other APs that a client has associated. UTM appliances could potentially attempt to discover these addresses, adding additional overhead.
You will find further details on this feature at https://documentation.meraki.com/MR/Other_Topics/MR_Access_Points_and_Magic_ARPs
To minimise the impact of Magic ARP packets, on the ARP Hit Rate, it is recommended to prevent unnecessary broadcast packets arriving at UTM network interfaces.