I have a client who is in a shared office environment with a lot of other wifi networks in play. They consistently get 2-3% packet loss when pinging outside of the network. As a measure of testing, we attached a host to a different wifi network in the same location and could not reproduce the issue. The one this that I notice about the configuration of this other network is that the PHY mode of the 5ghz radio is specifically set to 'N". My client would like me to configure the ZD and r500 AP's to use only the "N" mode as well, but I cannot find a way to do this in the ZD.
I see Jeremy, your's is a rather unusual use case... Have you evaluated your performance with 5G channels restricted to just lower or just upper range channels for packet throughput comparison? Also, compare your local network response times, not sure what bottlenecks might be on your WAN to 'outside of network' targets?