If you want to go straight USB, I’d recommend the ConbeeII. It’s a good, solid adapter that works well with ZHA, deconz, z2m, etc. However, if you want a LOT of devices (greater than 50), you’ll outgrow it quickly as it can only handle around 5 children and only a small amount of both normal routes and source routes.
I just got one of his coordinators recently and to be honest, it’s been REALLY good for my mesh. Personally, I like the CC2652p2 over the ESP version. I also have 2 of his routers. I know he is working his tail off right now to get more in stock. You can reach him here on the forum (@tube0013) and you can see my results here: https://community.home-assistant.io/t/zigbee-router-on-steroids
It’s not so much about the type of AP you have (I have the same), it is more about the channel interference between Zigbee and WiFi; They operate in the same 2.4ghz space and even the Unifi APs have issues with 2.4ghz interference.