Hi!
I have issues doing some net installs using various UniFi routers, including installing XOA over XCG-NG, which you are experts of! 
I first encountered the problem with the newish Raspberry Pi network install: when you boot a recent Raspberry Pi without any operating system, it now downloads and boots a Raspberry Pi Imager OS. With my UniFi routers, it downloads the image at only a few kilobits per second.
Copying the image URL displayed on screen, I can download the same file from another device connected to the same UniFi router at hundreds of megabits per second. If I connect the Raspberry Pi to the internet with a USB-C Ethernet adapter to my Google Pixel with tethering enabled, it downloads at dozens of megabits per second. And if I replace my UniFi router with the ISP router and keep the same fiber and copper cables, it also downloads at hundreds of megabits per second.
Same thing when I try to install XOA on XCP-NG (the hypervisor), with downloads going at 5 megabits per second, then hanging. I can download the same file from my PC at line rate.
I don’t understand what’s wrong, any clue?
(I’ve already asked on the UniFi community but nobody answered.)