My UniFi system has a " Auto-Optimize Network" feature that I needed off as it blocked broadcasts.
Determines and sets these options for optimum performance:
Block multicast and broadcast traffic for high density WiFi networks
Increase ARP timeout for high density WiFi networks
When enabled this overrides any manually set values.
The manually set values referred to are part of each wireless network definition under “Advanced Options”
Multicast and Broadcast Filtering
Block LAN to WLAN Multicast and Broadcast Data