Disclaimer: I've never used wireless uplink mode. The APs are linked by wired Ethernet, like god intended.
Mine too!
Wireless uplink works on the AP-Pro and their brethren, but it's my second choice.
The disc-shaped APs aren't really great as true Mesh units. They work best with wired backhaul and fixed, surveyed locations. The two types of Unifi Mesh APs that I've used are the outdoor units (big flat one and teeny double twig antenna one) and they work very well indeed for temporary/mobile locations. They automagically sort out their backhaul and routing between multiple units. They usually make a decent job of it, but you can tweak the setup manually.
If you're using multiple backhaul links with the mesh-aps, it's possible to create an inadvertent network loop/broadcast storm (on multiple VLANs, just for added fun). The Mesh-APs will sort it out but it can take a couple of minutes. Oops!
Now I rate-limit ICMP on the backhaul switch ports just in case.
Rookie error, but that's what you get when you rush.