Not sure if it's better to ask here or on the network engineering exchange, but since I'm looking for an Ubuntu-specific solution, here goes.
Configuration: Ubuntu 16.04, WiFi hotspot via hostapd, dnsmasq serving DNS/DHCP, Ethernet port and wlan bridged via /etc/network/interfaces
Problem: When a certain wired Ethernet device is plugged into the same network the WiFi hotspot becomes unusable. This device, a sensor, broadcasts UDP packets to 255.255.255.255 (the problem persists if I have it broadcast to 192.168.1.255). The symptoms are: wireless clients are unable to ping the hotspot or to obtain IP addresses (tcpdump shows DHCPDISCOVER and DHCPOFFER packets but no DHCPREQUEST or DHCPACK follow). Wired connections works without problems.
I worked around this by configuring the sensor to broadcast to a specific IP (e.g. 192.168.1.3) but several different devs on separate machines connect for development and it's inconvenient to change the setting every time we change devs/machines. I want to understand why this is happening (the bridged WiFi adapter chokes on retransmitting the UDP broadcast traffic?) and how I can prevent this from happening - no one will be consuming the UDP traffic over the WiFi link. Perhaps I need to configure the bridge to block UDP broadcast from going over the WiFi interface - without interfering with other UDP traffic like NTP or DHCP?