Wifi issues when running as a PI Zero hat?

[deviantintegral]

I've been having Wifi issues with a Pi Zero with a Z-Bee Duo attached to it. What I see is noticeable lags and drops when connecting over SSH. As well, the mqtt connection between my broker and zigbee2mqtt running on the zero will drop typically every hour or two. Unless the connection drops entirely, pings look fine. I ended up having to add a script that reboots the Pi when it can't ping the router, but that's a temporary fix at best.

At first, I figured it was an issue with my wifi network config (I have Unifi APs), but eventually I discovered that if I removed the hat that latency as measured by https://github.com/jacobsa/ssh_ping dropped significantly. I put it back on and the wifi issues came back. I was only able to test with it off for a few hours, so I'm not 100% sure I've identified the issue.

My next step is to connect the hat over USB instead, but I was short a USB OTG cable.

Has anyone else encountered issues like this? Any other ideas?

[deviantintegral]

I changed the connection from the HAT pins to the USB OTG cable, and Wifi is completely fixed. No drops and no lag for the past 5 days. The hat is still laid on top of the Pi board with no additional distance between them.