You have deployed a Juniper EX Series switch in the network.

According to the Juniper documentation1, when a switch receives a unicast frame destined to a MAC address that is not registered in the bridging table, it floods the frame out all ports that are part of the same VLAN, except the receiving port. This is the default behavior of a switch when it does not know the destination MAC address. The switch does not perform an ARP request, send an error message, or flood the frame to all VLANs. References: Understanding Unicast Flooding | Junos OS | Juniper Networks