I have a unifi system as well. I have multiple hubs on my network. I can tell you this is not normal. We need to get to the bottom of what is causing the issues on your network.
Are you using the new DNSMASQ option in the DHCP server options in Unifi or the original option?
I've responded to you via PM and hopefully we can get to the bottom of what's going on on your network. The only broadcast we do is respond to SSDP discovery requests.